Positive Pattern Platemaking Process (5)

3. Develop black ink and glue

1. In addition to developing black ink. Developing black ink is a kind of black ink made of oily substance and aqueous substance. It is an emulsified ink emulsified by oil phase and water phase substance. The developing black ink is applied to the printing plate surface. The oily substance is absorbed by the graphic part, and the aqueous material is absorbed by the blank part, which not only improves the lipophilicity of the graphic part, but also improves the stability of the blank part. Therefore, the developed black ink is applied to both the baked plate and the plates that have only been developed and dirty but not baked. In addition, the application of the developed black ink makes it possible to darken the text and also to check the quality of the print.

The oil phase material in the black ink is composed of terpene resin, turpentine oil, carbon black, and oil-soluble emulsifier. The waterborne substance is composed of gum arabic (or carboxymethyl cellulose), water-soluble emulsifier and water, commonly used emulsifiers. There is a 60 for the division and 60 for the Twain.

Terpene resin is a linker in developing black ink and is an unsaturated terpenoid. It can be dissolved in the mineral oil of turpentine oil, kerosene, gasoline, etc., and has excellent lipophilic properties. It is used to formulate black ink, has good affinity to the photosensitive layer, and has good ink receptivity. When used, terpene resins with higher boiling points are generally used because the low boiling terpene resins tend to volatilize when heated.

Turpentine is a good solvent for terpene resins and consists of cyclic hydrocarbons. It is volatile and flammable, and has a strong affinity for lipophilic substances.

Carbon black is a pigment in a black developing ink. It is an amorphous powder. It is insoluble in any solvent. Its dispersibility in the binder is also poor. Carbon black must be mixed into the terpene resin when preparing black ink. After grinding by the grinding roller of the grinding roller, it can be dispersed evenly.

Span 60 is also known as emulsifier-S or emulsifier S-60. It is the commercial name of sorbitan stearate and it is produced by the condensation of sorbitan and higher fatty acids. Nmousewheel="return bbimg(this)" alt="" src="" class="lazy" original="" onload="" border="undefined" /> Span 60 is a non-ionic surfactant and is a high quality water-in-oil (W/O) emulsifier. It has good emulsifying, dispersing and wetting properties and is soluble in water. It is used with Tween 60. Emulsification effect is more obvious.

Tween 60 is produced by the condensation of Span 60 with ethylene oxide. The molecular formula is Nmousewheel="return bbimg(this)" alt="" src="" class="lazy" original="" onload="" border="undefined" />, is a premium oil-in-water (O/W) Emulsifiers have good emulsifying, dispersing and wetting properties and are soluble in warm water and are often used with Span-60.

Gum arabic is a hydrophilic colloid that is used in developing black inks. Its function is to enhance the hydrophilicity of the blank. Gum Arabic has a higher market price and can be replaced with hydrophilic colloidal CMC (powdered methyl cellulose).

There are many formulas for developing black ink, one of which is listed below for reference.

Black ink formulation:
Pre-olefin resin 100g,
Turpentine oil 200ml,
Carbon black 50g,
One 60 3 g
Tween 60 l4g,
Gum arabic 8 g,
Water 1000ml.

The steps for preparing the developed black ink are as follows:

(1) According to the proportion of the formula, the terpene resin is dissolved in the turpentine oil at a temperature of 50-60° C., carbon black is released, and the mixture is uniformly stirred; then the mixture is ground into a grinding machine until the carbon black particle size reaches 4 to 1. When the carbon black is uniformly dispersed in the terpene resin at 6 μm, the grinding is stopped and the resin black ink is formed.

(2) According to the proportion of the formula, Dissolve Span 60 into water at 60°C, and mix the resulting solution with resin black ink to form oil phase material.

(3) According to the proportion of the formula, Tween 60 and gum arabic are dissolved in water at 60°C, and then phosphoric acid is slowly added dropwise, the pH of the solution is adjusted to about 5.5, and the aqueous phase material is formulated.

(4) Slowly inject the aqueous phase material into the oil phase material while stirring. At the beginning, the added water phase material is less, forming a water-in-oil type emulsion; with the increase of the amount of water phase material added, the emulsion When the viscosity of the emulsion rises, when the amount of water phase material in the emulsion reaches a certain amount, the viscosity of the emulsion drops sharply, and the water-in-oil type is converted into an oil-in-water type, and the developed black ink with good performance is obtained.

The developed black ink is prepared by the above method, and the emulsification speed is fast, the particles are fine, the water phase and the oil phase are uniformly dispersed, and it is not easy to separate and separate; the performance of the developed black ink is good and stable.

The application of the developed black ink is relatively simple. For baked plates, a gum arabic solution was first applied to the surface of the plate to make the plate wet, and then black ink was developed. For unbaked plates, the developed black ink can be applied simply by using a squeegee to remove the developing water and washing the water remaining on the plate. The black ink should be lightly rubbed with a slightly wet sponge. When the black ink is not dry, rinse the surface with a sponge while using water to clean the non-graphical ink completely. The printing plate can be printed or stored on the machine after being glued.

2. Glue. Gluing is the last processing step before printing on the printing plate, that is, applying a layer of gum arabic on the surface of the printing plate to make the hydrophilicity of the blank part of the non-image more stable and protect the plate from being dirty.

Gum arabic is a natural polymer compound, the main ingredient is arabic acid, the structure of arabic acid is

Nmousewheel="return bbimg(this)" alt="" src="" class="lazy" original="" onload="" border="undefined" />

writing The carboxyl group (-COOH) in nmousewheel="return bbimg(this)" alt="" src="" class="lazy" original="" onload="" border="undefined" ) is normally oriented The metal surface, while on the outer surface of the adhesive layer of the dried metal acacia, retains a large amount of OH (hydroxyl) as shown in Figure 9.

Nmousewheel="return bbimg(this)" alt="" src="" class="lazy" original="" onload="" border="undefined" />

Fig. 9 Adsorption of gum arabic on the surface of PS plate

Gum arabic is a reversible colloid that can swell in large amounts until it is completely dissolved. It can also gradually evaporate water and change from viscous to solid. Therefore, gum arabic can be formulated into a variety of concentrations of glue waves used to coat the layout, after the water evaporates and then converted into a solid, forming a strong cover sheet in the layout, to prevent the oxidation of the layout and dust in the air on the layout of the dirt . The concentration of the glue is generally 5°Be', that is, it is prepared by dissolving 100g of gum arabic in 1000ml of water. Gum arabic has a higher market price and can sometimes be replaced with chemical compounds such as CMC. However, if the stencil must be printed on the machine every few days, it must be glued with acacia.

After the gluing plate must be thoroughly dried, it can be used for printing. If the poorly dried printing plate is directly used for printing on the machine, when the water supply roller of the offset printing machine feeds the printing plate, the glue on the printing plate will be Rushing out, resulting in poor hydrophilicity of the printing plate.