- Essential conditions for film printing
(1) Polyethylene or polypropylene films with poor adhesion to ink usually require surface treatment.
(2) Excellent flatness without uneven thickness.
(3) No fish eyes, crystal dots, or lumps.
(4) Not adhesive.
(5) The requirements for the use of root shed products include transparency, etc. These properties should be fully studied and selected, including transparency, heat sealing, rigidity, shade heat bamboo, water resistance, drug resistance, and wrinkle resistance.
- The most suitable thin film for surface treatment of plastic film.
Plastic films with low surface “free energy” also have very little adhesion to oil content. This is because the amount of oil cannot attach to solid surfaces with lower “free energy” than itself. Therefore, ink with a wetting tension of approximately 3.6~4.2x 10-0N/cm (36-42dyn/cm) is clearly less likely to adhere to polyethylene films with a wetting tension of 3.1X10-4N/cm (31dyn/cm).
In addition, according to the principle of polarity equivalence, it is called ‘withered attachment’. Especially when the resin contains stabilizers and non-polar polyethylene, it is difficult to maintain the printing accuracy with additives such as polar oil phase opening agents and anti-static agents that are incompatible with the resin and contain a large amount of organic solvents. Therefore, before and after printing, it is necessary to treat the thin films such as ethylene and polypropylene with low board properties, good chemical stability, and not corroded by organic solvents.
- Printing ink for plastic film
(1) The basic composition of gravure ink for plastic film printing is mostly achieved through gravure printing. The basic composition of the ink is as follows:
Pigment or dye coloring agent 30-40%;
Physical constitution materials (pigments mixed with oil, Qingmou, etc.) 0-20%
Solid adhesive resin 10-40% 1
Volatile organic solvents 40~80%;
Plasticizers, plastic resins, paraffin dispersants, and other additives ranging from 0% to 5%
The above are only principles, and the specific composition should be determined based on the type and purpose of the film.
(2) The role of various components in ink
① Connecting material is one of the main components of ink. The connecting materials for gravure printing oil are generally made of synthetic resins, natural resins and their derivatives that have a bonding effect with the printed material, chlorinated rubber and its derivatives, and solvents. Basic requirements for resin:
1) Same or affinity with the printed object
2) Can change the surface properties of the printed material to generate polar groups or polar bonds;
3) Similar in physical performance to the printed object.
One of the main groups of synthetic rubber oxidation camphor technology and cyclization camphor rubber is the material, which largely determines the properties of the base. Due to the high requirements for physical and chemical properties of the materials used in the production of chemical ink.
The general principle for selecting pigments is: ① strong coloring power and bright colors; ② Good dispersion and good fluidity. Not precipitating; ③ Good chemical stability, no reaction or precipitation with resins, solvents, additives, etc.: ④ High oil absorption and stable color development. Soft and non damaging to the plate roller; ⑤ Can meet the requirements of printed materials for light resistance, heat resistance, and chemical resistance. At present, organic dyes are commonly used in ink, with a few using inorganic pigments.
