Lithographic plate and letterpress printing, intaglio printing plate is different, lithographic printing plate on parts and blank almost in the same plane, so the printing, can is blank parts with good hydrophilicity, after absorbing water can repel ink, and printing part have oil-wet performance, can repel water, and adsorption ink. Printing when it used its features, wetting with water on the plate first and make the blank part of the adsorption of water, then on the ink, for blank parts have adsorption of water, can't adsorption inks, and adsorption ink printing part, after the plate on the printing part have ink can be printed.

Today the offset lithography, most of them adopt the graphic on the plate first transfer to the rubber cloth roller, blanket again by transfer to the paper (substrates) on indirect printing method, the lithographic offset printing. Because of the elastic rubber cloth, can print fine graphic.

 

An overview,

 

Lithographic plate is how to make the graphic on the plate with good hydrophilic part blank, has the stable hydrophilic. According to the use of different materials and methods, there are many kinds of plate making method.

 

Classification of 1.

 

(1) according to the classification of plate are: tablets, zinc plate, aluminum plate, paper, etc.

 

Slab is the earliest lithographic plate, stone plank bulky, can only be printed directly, so it is no longer used.

 

Zinc plate and aluminium plate is now commonly used materials. Paper is developed in recent years, used for electrostatic plate making, printing prints and light printing quantity not too much.

 

(2) according to plate making methods of classification are: painted version, turning plate, namely, pre-coating version, multi-layer metal coated edition offset, gravure, static version, dry offset, and so on.

 

Painted version roller lithographic plate making method of the original use ink manual car paint build printing part on the plate. No longer in current use.

 

The first classification (3) according to the plate surface are: lithographic, relief, intaglio.

 

2. Plate with light-sensitive materials

 

(1) bichromate light-sensitive materials

 

Dichromate photosensitive material is raw chromate and mixture of high polymer material, after drying has sensitive performance. That is commonly used in lithographic plate burning polymer material has: protein, polyvinyl alcohol, etc.

 

: in dichromate ammonium dichromate. Dichromate has toxicity, so when use should pay attention to safety.

 

(2) the diazo photosensitive material

 

Diazo photosensitive material is composed of diazo or pile of nitrogen compounds and natural resin of photosensitive resin. Photosensitive resin by light effect, can cause photochemical reaction, make its molecular structure changing decomposition or teng, polymerization, when faced with the solvent to produce biological changes. Therefore, can be used for plate burning, etc.

 

Second, the homemade lithographic plate method

 

1, metal lithographic plate method

 

Lithography with a metal plate, with zinc plate and aluminium plate is given priority to, also useful iron or copper. This is determined by the characteristics of the lithography, lithographic plate, should not only highly hydrophilic and had good hydrophilicity, actually not that want to materials processing. Generally the lipophilicity of the metal is strong, weak hydrophilic. Commonly used metal lipophilic order is: the iron > > > > > nickel chrome aluminum zinc.

 

Can be seen from the above order, the copper lipophilicity, best and worst hydrophilicity, chromium the hydrophilicity of the best and the worst, but hydrophilic zinc and aluminum as lipophilicity, but also has certain hydrophilicity, after special treatment, can improve lipophilic and hydrophilic, so used in flat printing zinc plate and aluminium plate, copper and iron are used to produce multilayer metal version.

 

(1) version of material surface treatment

 

Surface treatment is to make the printing plate part establish good foundation, expand the space of specific surface. To enhance the adsorption ability, but to blank parts, is conducive to ChuMao moisture and reduce the surface tension, for used plate, there is also a role is to get rid of the graphic on the old.

 

Plate surface treatment is to build sand, sand objective methods are: mechanical method, electrolytic process, sand blasting method and the method of corrosion, is usually adopted mechanical grinding method.

 

Mechanical plate grinding method in a plate grinding machine grinding plate formed by sand. Plate grinding machine consists of a millstone, eccentric shaft, the base. Put inside mill plate, put on the grinding balls, mill by eccentric shaft drive centrifugal rotation of the grinding ball in the columns of the scroll, and water and sand, and water wetting effect, grinding ball grinding pressure to plate surface, grinding effect, makes the plate surface of fine sand. Sand purpose depth, thickness and the size of the grinding ball, specific gravity and grind arenaceous, fineness, and the dosage of the water hardness, stroke of the plate grinding machine, grinding time.

 

Sand blasting method is the use of air compressors, compressed air will be sand into the sand is formed on the plate. Sand blasting method with high efficiency, but quality is not easy to control, poor uniformity.

 

Corrosion method using chemical etching liquid corrosion on layout and form sand. Corrosion method has the advantage of avoiding the mechanical grinding version of the noise, reduce the physical labor intensity, but the high cost, low efficiency, less in the quality is not stable, practical.

 

Electrolysis aluminum plate using electrolytic sand mesh, using alternating current (ac), the electrolyte with dilute hydrochloric acid, when aluminum plate as cathode, the hydrogen ions in solution on the aluminum plate accept electronic, generate hydrogen and escape, when the anode for aluminum plate, aluminum atoms emit electrons, ions into the electrolytic solution, in under the action of repeated alternating current (ac), reaction alternates, sand the resulting, using this method can obtain fine uniform sand.

 

(2) protein edition print

 

The printing method is to use egg itself high polymer material, mixed with dichromate press as a coating solution, suitable for plate burning, from Yin as negative version of the so called protein, its craft has called Yin like plate burning.

 

Sand purpose to grind metal plate, and then to former corrosion, its purpose is to remove the version of the layout of residual mud and oxide film. Before at the same time, the corrosion liquid is acidic solution, can make the layout by slight corrosion with sand purpose, form very small uneven, further expand the layout of the specific surface area, increase the adsorption capacity.

 

Metal surface after grinding and former corrosion after processing, such as dispersed protein coating solution drying, and Yin as the film contact exposure, due to the transparent part by part of the film, so the graphic part of photosensitive layer by light irradiation, photochemical reaction, make the photosensitive layer glue hardening, form the printing on the plate. Coating after developing ink, make the hardening of the rubber to absorb developing ink, with oil wet performance, and the blank part is opaque part of the film, can stop light through, so at the time of exposure photosensitive layer by light irradiation, colloid not occur degeneration, still can dissolve in water, dissolved by water in the developing, leaving only hardened rubber on layout, namely printing part.

 

Protein version printing process is: the former corrosion - situ photosensitive liquid - exposure to developing ink rub, development - after corrosion - glue.

 

Protein version after exposure, rub on a layer of uniform and fatty strong developing ink can. Flush when developing, and layout on cotton light, made by the light rubber to remove role. Not after the effect of corrosion is completely eliminated by light rubber, prevent dirty, at the time of the printing of the gluing is to make the plate on the blank part has good hydrophilicity, and prevent the oxidation of the layout, build a stable blank parts.

Protein printing part is the basis of the photosensitive glue line, with strong sex fat developing ink, printing form hydrophilic parts. Printing parts slightly higher than that of blank, foundation is only part of the hardening of the rubber, so this kind of plate seal strength and abrasion resistance is low, especially can not adapt to the requirement of high speed printing machine. In addition, by easy hypertrophy, so less in current use. Its advantages are simple operation and low cost.

 

(3) flat gravure plate burning

 

Flat gravure printing is the use of pva mixed with dichromate as a coating solution, made of Yang like film printing plate, so also called polyvinyl alcohol, its craft is also called Yang like plate burning. The plate making method to enhance the resistance of the graphic part force, make the image under the concave 3 ~ 5 microns, is called flat intaglio (deep etched plate).

 

Flat intaglio printing process is: the former corrosion to dispersed coating solution, the exposure and development - corrosion - rinse - air - tracing glue to the base paint, brush after developing ink - in addition to the film - corrosion and gluing.

 

Metal plate mill version, before the corrosion process and dispersed liquid photosensitive after drying, and Yang as the film contact exposure, due to the graphic part is opaque, after exposure, photosensitive rubber not effect, by light and transparent part is blank part of the plate, photosensitive rubber after exposure by light effect and hardening, has the corresponding corrosion resistance, can make development and blank parts from erosion corrosion.

Enhancement is the page layout is not light effect of rubber remove, can make the graphic part thoroughly exposed on the metal board. In order to remove both graphic part respectively, and can protect by light rubber, developer to calcium chloride, zinc chloride, lactic acid, etc. The length of the developing time and the temperature of the surrounding air, humidity and the concentration of the solution.

 

Corrosion is that exposure to the metal printing part, on the screen with acid corrosion, and make graphic form micro concave part, corrosion in the liquid composition is similar with the developer, only acid is stronger, is acid (hydrochloric acid) instead of weak acid (lactic acid).

 

Metal version by flushing remove corrosive liquid, dry, to check whether there is blank space exposing part of the metal surface, and if there is a will form the dirt, so must be bared metal surface with plastic cover, called glue around it.

 

Base paint is in the printing section of the metal board, build a strong oil-wet layer material. , it can serve as part of the increase printing lipophilicity, water resistance, resistance to acid grinding in time, so the base paint performance directly affects the quality of the plate, coated base paint wants even, thickness should be appropriate, prevent to produce streaks.

 

Wipe after developing ink is on the base paint, the thermal drying process, its purpose is to protect the base paint layer, prevent the acidic liquid in the process of coating erosion of the graphic base paint layer, and increase the oil-wet graphic performance. In addition, the development of the black ink, but also clearly shows that the depth of the graphic, level, easy to identify the quality of the graphic.

 

In addition to the film work simpler with acid in addition to the film liquid poured on the layout, rubber white gradually, fell off the page, and then rinse with water, clean with a brush, layout of rubber will cleanse, otherwise when printing up dirty.

 

After the corrosion, glue to establish stable blank parts.

 

Flat gravure process more complicated than the protein version, but on the plate by fine quality, good abrasion resistance, resistance to seal force in 3 ~ 50000 printing, was a major domestic lithographic printing method. With the popularity of precoating version (PS), flat gravure is gradually being replaced.

 

2. The multilayer metal lithographic plate method

 

Multilayer metal sheets (multi - metal plate) is made up of 2 or 3 layers of different metal combination of lithographic plate. Printing part and blank part respectively choose different metals, metal printing part adopts hydrophilic, such as copper. The blank part adopts hydrophilic metals such as chromium, nickel, etc. Multilayer metal version of the metal layer can be divided into bimetal plate and three layers of metal.

 

(1) double metal version

Is another plating metal on metal version of the foundation, become the second floor. And according to the types of version of the base film, decide what the second plating metals, such as Yang like film plate burning, the chromium plating layer on copper plate; From Yin as negative plate burning, it should be in aluminum or stainless steel plate coated with a layer of copper. Level of coating thickness is 5 ~ 10 microns.

 

(2) three layers of metal

 

Version is based on iron base, in the board base on several micron copper layer or chromium plating layer, then electroplating a layer of chromium layer or copper plate base in addition to the use of iron, you can also use the zinc plate, aluminum plate, stainless copper plate and so on. Using film can be Yin like film, also can use Yang like film. If from Yin as negative plate burning, the third layer copper plating layer or multilayer flat was letterpress, if use Yang as negative plate burning, the third layer of chromium plating layer, the corrosion is multilayer flat intaglio.

 

Three layers of metal version of the general technological process is: the mill version - cleaning - copper - chrome - plating pretreatment to dispersed coating solution, the exposure and development - tracing glue - secondary exposure to corrosion, in addition to the film - inking - glue.

 

At present, the domestic multilayer metal version of the printing process, and basically flat intaglio printing process, plate burning, from Yang as negative photosensitive liquid using polyvinyl alcohol dichromate coating solution, the difference is dispersed in the photosensitive layer thicker, exposure time should be longer and have better corrosion liquid acid, therefore, in order to enhance the acid resistance of photosensitive hardening layer, after enhancement, corrosion should be exposed again before. When printing part of chromium layer corrosion after removing, in sulfuric acid solution to remove blank portion of the hardening layer, then the side wipe mention ink agent (mention ink agent's role is to remove oxide layer on the surface of the copper, copper is in active state, more conducive to ink absorption), while developing ink, inking process finished, brush a layer of protection glue again.

 

With multilayer metal version of the printing part is copper, its oil-wet performance is very good, blank part is chrome, has good hydrophilicity and high wear resistance, so it can reduce the printing the transfer of water temperature, make the printing on the paper printing ink layer is thick, bright luster, and improve the quality of printed matter. Resistance is printed force can be as high as 1 million, suitable for print run large offset rotary press.

 

Multilayer metal version in production is more complex, need a complete set of electroplating equipment, and to use many non-ferrous metals, the cost is high, so in terms of use. Abroad for precoat type multilayer flat gravure materials for sale.