Development and Application Technology of Fluorescent Security Ink for Plastic Packaging (I)

1. Binder screening

The linking material is a fluid component in the ink and is responsible for the connection of a solid powdery substance such as a pigment to form a pastey colloid after polishing and dispersion, and the function of drying and fixation on the surface of the substrate after printing. The rheology, viscosity, viscosity, drying and printability of inks are mainly determined by the properties of the binder. Therefore, in order to obtain high-quality inks, high-quality linking materials should be manufactured first.

The commonly used binder resins for plastic printing inks are mainly polyamide resins and acrylic resins.

1) Polyamide resin

Polyamide resin commonly known as nylon, from the polycondensation of polybasic acid and polyamine, in which a linear polyamide resin formed by the polycondensation reaction of diamines and dibasic acids, is the basis of the reaction of the polyamide resin.

Polyamide resins are reactive and non-reactive. The reactive polyamide resin is in the form of a liquid or a semi-solid and must be added with a bisphenol A epoxy resin before it becomes solid. The non-reactive polyamide resin is a thermoplastic resin and can be decomposed into a film. Non-reactive polyamide resins are mainly used in the production of printing inks, and plastic films are printed with the plastic gravure inks prepared therefrom, which has strong adhesion and good dryness, but the cost is high and the solubility is poor. Most polyamide resins are insoluble in ethanol and only dissolve in mixed solvents prepared with toluene, xylene, isopropanol, ethanol, etc., and these resins often freeze at lower temperatures, affecting the ink mixing performance and printing. Fitness. Therefore, improving the solubility of the polyamide resin and overcoming the freezing phenomenon of the resin is the future direction of research and development.

The alcohol-soluble polyamide resin has a pale yellow, light and transparent appearance, an acid value of less than 6, an amine value of less than 5, a softening point of 107±3° C., and a 30% alcohol ester mixed solution, which can be stirred and dissolved at room temperature. At 25°C, the viscosity is 25～50mPa·s, suitable for high-speed gravure printing and flexo printing.

2) Acrylic resin

Acrylic resin is made of condensing ethylene polymer. Acrylic acid and its derivatives all have unsaturated double bonds, high activity, and easy to polymerize to produce high molecular weight thermoplastic resin. Copolymers of acrylic acid and other substances have different forms such as solid, liquid, and latex. The inks made of it have the advantages of lightness, transparency, strong adhesion, hard conjunctiva, and friction resistance, and their disadvantages are high prices. With the development of photocurable inks and photocurable coatings, the use of acrylic resins in the ink manufacturing industry will also increase.

After repeated research and analysis, it was finally decided to use a non-reactive polyamide resin as the binder resin for this ink, and by adding experimental additives to the binder, the binder resin was modified to improve the connection. Mixture of materials and fluorescent pigments and their adhesion to the surface of plastic film.

2. Solvent screening

Plastic gravure ink common solvents are isopropanol, toluene, xylene, n-butanol, ethanol, ethyl acetate and so on.

Solvents are important components of plastic gravure inks. They have solubility and volatility. The volatilization rate is an important factor in determining the drying speed and printing quality of volatile inks. The evaporation rate of the solvent is slow, and the reproducibility of the printed image is good. However, if the volatilization rate is too slow, if it is not thoroughly volatilized on the printed matter, the ink layer is likely to be adhered. On the contrary, if the solvent in the ink volatilizes during the printing process, If it is too fast, it will result in white whitishness, sticky rollers, etc., and it will hide potential troubles of ink layer sticking back. Therefore, the choice of solvent is very important. Choosing a solvent for plastic inks usually considers the following factors:

1) The speed of the printing press. The higher the speed of the press, the faster the evaporation rate of the solvent is required;

2) The structure of the drying system;

3) the characteristics of the printing materials;

4) Indoor temperature and relative humidity;

5) Ensure that the solvent does not corrode the plate;

6) Good solubility without any mechanical impurities and free acids, alkalis and moisture;

7) Can not react with other components in the ink;

8) Small odor, low toxicity, and volatile matter should meet the requirements of environmental protection; the ink used for food packaging and printing should be practically non-toxic;

9) Storage stable, no decomposition, no moisture absorption;

10) Low prices and abundant resources.