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The difference between surface and internal printing inks
Release time:
2022-06-23 18:04
Ink is an indispensable material for the decoration and packaging of printed goods. Through printing, the packaging surface becomes beautiful, colorful, exquisite and attractive. In recent years, with the rapid development of the printing industry, various plastic and paper packaging printings have been continuously improved, and the requirements for product packaging grades are getting higher and higher. Composite flexible packaging printing is different from general packaging printing, that is, the former is inner printing, and the latter is surface printing. The inks used in both are called inner printing ink and surface printing ink respectively. We must analyze the difference between these two inks before printing. It is of great significance to use them correctly. Most of the inks in my country are composed of 20% to 40% of binders, 5% to 15% of pigments, 40% to 60% of organic solvents and 0% to 5% of additives. The binder is a bonding resin and a key component of the ink. It bonds the pigment to the printed material, plays an adhesion role, and makes the ink shiny. The pigment determines the color type. The solvent dissolves the resin, adjusts the viscosity, adjusts the drying speed, and improves the wetting effect on the printed material. Additives improve viscosity, weather resistance, aging resistance, and increase gloss. The following is a brief analysis of the differences between inner printing ink and surface printing ink summarized by our factory over the years.
Differences in binders
The binder of surface printing ink is mainly polyamide resin, which has good adhesion and gloss, but is not suitable for high temperature conditions and has poor fastness when compounded. The binder of non-cooking inner printing ink is mainly chlorinated polypropylene. Foreign countries also use nitrocellulose and vinyl chloride-vinyl acetate copolymer resin. Domestic Jinlong GD-1 and Dongfang 200 belong to this category. The binder of high-temperature cooking inner printing ink is polyurethane. When used, a certain amount of hardener is added, the two liquids are mixed, and the reaction is cross-linked, such as Dongfang 300.
Differences in solvents used
The solvents used in surface printing ink are mainly xylene and isopropyl alcohol. The solvents of general inner printing inks are mainly toluene and ethyl acetate. The high-temperature cooking inner printing ink is mainly acetone, ethyl acetate, etc. The solvent of the back printing ink is suitable for high-speed printing, the solvent has a fast volatility, and the solvent residue is particularly small.
Difference in wear resistance
Since polyamide resin has good softness and great elasticity, the added additives make it have good wear resistance and improve it, and it is more solid when it collides with external objects. The chlorinated polypropylene resin of the back printing ink has particularly good rigidity and poor wear resistance. Since it is back printing, the wear resistance requirement is correspondingly lower.
Difference in different auxiliary materials
Due to the difference in connection, the auxiliary materials and additives of the surface printing ink and the back printing ink are also different. Dehydrated apple and kiwi fruit acid esters are often added to the surface printing ink to improve adhesion, increase gloss, and increase viscosity. Various pigment dispersants, enhancers, defoamers and other additives are also added to the back printing ink.
Difference in printing process
The back printing platemaking process is exactly the same as the general platemaking process, but the image on the printing plate during the surface printing platemaking is a reverse image, and it is a positive image after printing, while the back printing plate image is a positive image, and it is a reverse image after printing. The printing speed of surface printing ink is slow, while the printing speed of back printing ink is faster than that of surface printing. The printing color sequence is also different.
How to get rid of the pollution from ink
After the solvent in the ink evaporates, the main pigments, resins and additives left in the printed matter are mainly pigments, resins and additives. If it is a printed matter used for food and medicine packaging, it is best not to come into direct contact with food. Because the oils, alcohols and esters (in wine and spices) in food may dissolve the resin in the ink. Then the food may be contaminated by resins and pigments. In particular, solvent-based, water-based and other volatile drying inks are more likely to be redissolved. UV ink may be better, because it is light-cured, unlike the oxidation conjunctival drying of offset ink, and it is less likely to be redissolved after drying.
When reading books and newspapers, people should overcome the bad habit of using fingers to dip saliva from the tongue to avoid bringing ink into the mouth.
Application
Composition and application of gold and silver printing inks
Like other inks, gold and silver inks are mainly composed of two parts: pigment and binder. Simply put, gold ink is made of gold powder and gold oil, and silver ink is made of aluminum powder and silver oil.
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