Various lithographic plates

Commonly used lithographic plates include PS plate, gravure plate, protein plate (plano plate), multi-layer metal plates and the like. The surface of each printing plate is composed of a lipophilic and hydrophobic graphic portion and a hydrophilic, oleophobic blank portion.

First, the PS version of the plate making process

The PS version is an abbreviation for Pre-Sensitized Plate.

The base plate of the PS plate is a 0.5mm, 0.3mm, 0.15mm thick aluminum plate. The aluminum plate is subjected to electrolytic roughening, anodization, and pore sealing, and a photosensitive layer is coated on the surface of the plate to make a pre-coated plate.

According to the photosensitive principle of the photosensitive layer and the plate making process, the PS plate is divided into a positive-type PS plate and a negative-pattern PS plate.

The positive plate type PS platemaking process is:

Exposure → Development → Dirty → Revised → Roasted Plate → Painted Ink → Glue

Exposure is the positive side of the positive film with the emulsion side of the PS plate with the photosensitive point of view, placed in a dedicated Shaibanji (see Figure 4-19), vacuum pumping, open the light source of the plate, The printing plate is exposed to light, and the photosensitive layer, which is not a graphic portion, undergoes a photodecomposition reaction under light irradiation. The commonly used printing plate source is an iodine lamp.

In the development, the exposed PS plate is subjected to a development treatment with a dilute alkaline solution to dissolve the compound generated by the photodegradation reaction in the visible light, and a photosensitive layer having no light is left on the plate surface to form an oleophilic graphic portion. The development is generally performed in a dedicated developing machine.

In addition to the dirty is the use of dirty liquid, the layout of the excess lines, adhesive paper, positive film negatives left on the edge of the traces, dust, dirt and other clean.

Patching is based on the developed PS plate. For various reasons, it is necessary to add graphics or patch the plate. There are two commonly used patching methods. One method is to apply a photosensitive liquid on the surface of the sheet again, supplementing the sun requires additional graphics, and another method using a repair liquid to fill the pen.

The baking version is to expose, develop, remove dirt, repair the plate, and apply the protective liquid on the surface, and place it in a baking machine. Bake at a constant temperature of 230 to 250° C. for 5 to 8 minutes to take out the printing plate. After being cooled naturally, it is developed again with developer, and the remaining protective liquid on the plate is removed and dried with hot air. After the roasting plate is processed, the resistance force can be increased to over 150,000 impressions. If the printed quantity is less than 100,000 prints, the PS plate does not need to be baked.

Coating Developer The main application of adhesive is the graphic application of developing black ink on the printing plate, which can increase the adsorption of the ink on the graphic, and it is also convenient for checking the printing quality.

Gluing is the last process of PS plate making. That is, a layer of gum arabic is coated on the surface of the printing plate to make the hydrophilicity of the non-graphical blank part more stable, and protect the plate surface from being stained.

PS version of the sand fine, high image resolution, the formation of a clean and smooth network, with a good tone, color reproduction.

The PS plate that will be used in printing will remove the remaining ink and photosensitive layer on the plate surface, and re-coat the photosensitive liquid on the original aluminum plate to form a new photosensitive layer, which can be re-formed for proofing or the official printing plate. . This method of remaking a PS plate using a used PS plate aluminum plate base is referred to as reproduction of the PS plate, which makes the aluminum plate base reusable, so that the PS plate is the plate most used in lithography.

Second, other flat plate making process

(a) Multi-layered metal plate

In accordance with the shape of the concave or convex figure, it is divided into a flat gravure version and a peaceful relief version. The copper metal is chrome-plated to make a two-layer gravure plate. The iron metal is plated with copper and then chrome plated to make a three-layer gravure plate.

The metal plate is a metal with good lipophilicity and a metal with good hydrophilicity. A stable graphic portion and a blank portion are formed on the plate, and the printing force is high. However, the platemaking cycle is long, the cost is high, and the tone and color reproducibility are not as good as those of the PS plate. It is suitable for the printing of large quantities of banknotes such as shading and packaging materials.

(b) Flat intaglio

It is a printing plate that has been dried on the positive plate. The plate making process is:

Grinding → Pre-corrosion → Applying photosensitive solution → Printing → Developing → Corrosion → Waxing wax → Removing film → Gluing

After grinding and pre-corrosion of the zinc plate or aluminum plate, the surface of the photosensitive adhesive coating, drying and positive negative film with a printing machine, vacuum suction after exposure. The photosensitive film on the blank part of the printing plate is hardened by the photochemical reaction caused by light irradiation. The unsensitized film of the graphic part is removed by development, the metal surface is exposed, and the metal is slightly corroded by the etching solution, and then coated with the pro The base paint (wax light) of the oil is formed by the oil-and-hydrophobic graphic part.

After the intaglio graphic part was formed, the plate-hardened photosensitive film was removed and treated with a phosphoric acid solution, followed by hydrophilic gum arabic, and a hydrophilic, oleophobic blank was also formed.

The gravure is gravure version, the photosensitive adhesive used is composed of polyvinyl alcohol, ammonium dichromate and other materials, the plate making process of the plate is complex, the quality is not easy to control, and the tone and color reproducibility are not as good as the PS version, so the quantity used is Is.

(c) Protein version

The protein plate is coated on a metal zinc plate that has been ground, coated with a layer of photo-sensitive solution made of protein, ammonium dichromate, and ammonia, dried, and placed in a printing machine together with the negative plate. exposure. Because it is a negative-printing printing plate, the photo-textured layer, which is partially light-transmitting and light-irradiated, is hardened, and a oleophilic graphic is formed. After rubbing the developing ink, water is used to wash off the blank film of the unseen light and corrosive treatment, so that the blank part has hydrophilicity, and finally the gum arabic is coated.

Protein version has low cost and simple operation. However, due to the poor acid and alkali resistance of the hardened photosensitive layer, it has a high publication surface, and it has a low printing power. Generally, it can only print more than 10,000 sheets. It is suitable for printing with a small number of printing marks. Products, therefore, the use of this printing plate is limited.

(d) Zinc Oxide Paper Base

Is a zinc oxide photosensitive semiconductor material, directly coated on a paper base (or plastic film base) made of a photosensitive plate. The format of the plate is eight open.

The zinc oxide paper base plate was made using an electrostatic platemaking machine. The general operating procedure of the machine is:

Warm up after power-on → Place originals → Place photo-sensitive version → Charge → Exposure → Develop → Revise edition → Solid edition → Hydrophilic treatment

Charging is the key operation for the photoconductor to obtain photosensitivity. Under the cooperation of the charger, a certain surface voltage can be obtained on the surface of the photoconductive film.

Exposure is through the optical system, in the charged zinc oxide paper plate, so that the surface according to the image of the tone, resulting in a degree of attenuation, the formation of electrostatic latent image.

Zinc oxide paper base plate, generally using magnetic brush development method, so that the positively charged developing toner is adsorbed on the electrostatic latent image with a negative charge, forming a visible image.

After the plate is developed, the bottom ash is carefully blown away with a suction pen, and unnecessary toner is removed to correct the plate.

Use electric heating wire, infrared light bulb, iodine tungsten lamp and other heat sources to heat the revised layout text to make the toner hot melt and fix it on the paper plate. The temperature is generally controlled at 120°C～140°C and the time is about 20～30. second.

In order to ensure that the blank part of the printing plate does not become dirty during the printing process, a mixture of potassium ferrocyanide and white tannin glue is applied to the plate surface, and the printing plate is subjected to a hydrophilic treatment.

Zinc Oxide paper base plate, the plate making process is simple, the speed is fast, the cost is low, the resistance force is generally 5000, so it is widely used in the small offset press of the light printing system.


Source: Bison