Composition and performance of gum Arabic
Yang Tu due to the low risk of establishing a recycled plastic particle factory, the blank part of the PS version is metal oxide Al2O3, which is a high-energy surface (0.7j/㎡), which can be well wetted by the fountain solution during printing. At ordinary times, it is easy to react with O2, N2, CO2, etc. in the air, and it is easy to generate oxidation points, which reduces the surface energy, deteriorates the wettability, and absorbs impurities, oil stains and other dirt, When printing, it is difficult to clean and cause dirt. Because of this, it is necessary to protect the blank part, make use of the film-forming property of glue (low-energy surface of polymer compounds), isolate the layout from the air, prevent the layout from being scratched, store it away from light, ensure the hydrophilicity of the blank part itself, and endow the blank part with better hydrophilicity
in order to be suitable for plate making and printing, there are certain requirements for this kind of protective glue
reversible colloid. The protective glue evaporates and dries to form a film colloid. The printing water roller can dissolve the glue film and print normally without hand washing.
it has a certain viscosity, is easy to apply, and can be well adsorbed by the blank part.
it has good film-forming property, and will not generate pinholes after drying.
it does not damage the PS version, and is neutral or weak acidic (ph=), It is not easy to decay and deteriorate
commonly used protective gums are Arabic gum and new polymer gum
engineering parts Arabic gum is a natural polymer compound, commonly known as peach gum, which is a secretion of tropical acacia trees. It can be cut and collected from the stems and branches of the tree, and formed by dehydration and drying. It has different shapes and sizes, including round, egg shaped, worm shaped, and is a white, light yellow or brownish yellow transparent solid, The lighter the color, the better the quality; There are fine and irregular wrinkles and concave convex cracks on the surface. The texture is hard and brittle. It has strong luster after cracking. Its density varies according to different places of origin, roughly between 1.34 and 1.62, and the water content does not exceed 15%. Peach gum has great differences in properties and is easy to deteriorate, so it is not suitable to store
composition and properties of Arabic gum
gum Arabic is an organic high molecular carbohydrate, belonging to polysaccharides. It is generally composed of D-galactose, L-arabinose, L-rhamnose and D-glucuronic acid, with a relative molecular weight of about 220000 ~ 300000. The chemical molecular formula is xcooh xcook (xCoO) 2ca (xCoO) 2mg. Among them, X is a sugar (cah13o5) n composed of carbon, hydrogen and oxygen elements. N is a great value, which is Arabic acid (x COO), calcium arabite [(xCoO) 2ca] Magnesium arabite [export the test results to excel and print the test report (xCoO) 2mg], a mixture of potassium arabite (xcook), English name arabicgum, soluble in water, insoluble in ethanol and most organic solvents
(1) hydrophilicity. The molecular structure of gum Arabic is composed of -cooh and -oh connected to the same hydrocarbon bond. The factory adopts the earliest high-temperature polymer customized design, mold, testing and processing expertise to manufacture various key components. These two functional groups are hydrophilic, and hydroxyl
(-oh) is easier to accept water than carboxyl (-cooh). Therefore, when Arabic gum is dissolved in water, it will dissolve for about 72 hours according to the process of diffusion, water absorption and swelling to form a molecular solution of the dispersion system, in which the hydroxyl group in each molecule shows great hydrophilicity, and can automatically dissolve in water into a single-phase stable system, which will neither condense nor precipitate, and can ensure the stability of the dispersion system for a long time
(2) weak acidity. Because peach gum contains Arabic acid (xcoh), its aqueous solution is weakly acidic. It neutralizes with alkali, reacts with metal or metal oxide to form arabite, releases hydrogen, and has good adsorption
prone to corruption. In the hot environment (the use temperature of Arabic gum is - 5 ℃ ~ 45 ℃), yeast is easy to reproduce and ferment in Arabic gum liquid, which makes Arabic acid free and changes the colloidal property. This is the general property of sugars, and also the reason why Arabic gum foam and its use time will be rotten. With the increase of temperature, the acidity will increase, the corrosiveness to the metal plate will increase, and it is easy to drop the plate. In serious cases, Al2O3 will fall off. This should be paid special attention in summer to keep the protective glue away from high temperature
in practice, Arabic gum is the main component of hand mixed protective gum
new polymer protective adhesive
on the market, regular manufacturers sell mostly polymer adhesive. The main ingredients are water-soluble resins, phosphate inorganic salts, surfactants, alcohols, etc. the composition of different brands of protective adhesives is different