Packaging printing security ink screen printing process

First, thermochromic ink screen printing process 1. Thermal ink

Thermal ink is a kind of special ink that can change color with temperature. It can display different colors at different temperatures. It is also called temperature-induced color-changing ink. It is divided into inorganic, organic and liquid crystal. Inorganic heat-sensitive ink materials are heavy metal salts, which have strong toxicity in themselves, and the material has poor affinity with ink binders, poor printability, and has been eliminated in anti-counterfeit printing. Organic materials are low temperature, non-toxic and suitable for printing. Liquid crystal ink is currently the technology that people are most interested in and difficult to grasp. The principle is to change the optical properties caused by the lattice changes of the material. To date, thermal ink still occupies a large proportion in security printing.

The main components of thermal inks are color changing pigments, fillers and binders. The color change function mainly depends on the color changing pigments. The color change before and after the heating of the pigment is very different, and is used as the basis for judging the authenticity of the ticket. It is well known that there are many varieties of pigments that undergo color changes due to heat, but the pigments used as thermal ink must have the following conditions:

1 Sensitive to the effect of heat, there is a fixed color at room temperature, and the color changes rapidly when the temperature is reached;

2 There are obvious limits of color change, that is, the color temperature range should be narrow, and the color difference before and after the color change should be large;

(3) Small influence from the external environment, stable performance in light and humid weather conditions, no decomposition, no fading.

2. LCD ink screen printing process

(1) Liquid Crystal

Liquid crystals have the fluidity and surface tension of the liquid and have the optical properties of the crystal. The optical properties of the cholesteric phase liquid crystals can change with changes in temperature. The cholesteric liquid crystals are formulated into mixed materials of different temperature-changing temperature zones and then made into microcapsules. These liquid crystal microcapsules can be printed by incorporating them into the ink. . In the case of liquid crystal printing, it is not possible to crush the capsule, so it is most suitable to use screen printing with a small printing pressure.

(2) Example of Liquid Crystal Ink Method

Mix 1 part of gelatin and 12.1 parts of distilled water into an aqueous solution. Add 70% of the liquid crystal melt of cholesterol acrid salt, 25% cholesterol, 5% cholesterol, and cinnamate to 55°C. Then use a blender. It is dispersed into particles with a diameter of 15-30 μm. In a separate container, 1 part gum arabic and 95.6 parts distilled water were blended by mass, the temperature was controlled at 55°C, and the gelatin aqueous solution was gradually added to adjust the pH to 4.85. When the mixture was cooled to 15°C, a 25% pentylene glycol aqueous solution was mixed in, and the mixture was washed and dehydrated with a dehydrator to obtain a concentrated capsule slurry, and a 10% aqueous solution of polyvinyl alcohol was mixed to prepare a liquid crystal microcapsule ink.

(3) liquid crystal ink screen printing process

1 Generally, a nylon mesh or a polyester mesh can be used to make a screen. If the printing plate requires a large amount of ink, stainless steel mesh can be used. The mesh size is generally 100 to 175 mesh/inch, and the selection is based on the ink microcapsule diameter and ink layer thickness requirements.

2 When using plate-making, sensitive emulsions should be used.

3 The printing plate should be filled with enough ink at a time. It is best not to fill ink in the middle to prevent foaming.

4 When the phenomenon of blocking foaming is found in the printing, it is necessary to stop the machine immediately and completely clean the screen with alcohol.

5 The printing pressure should not be so great as to crush the liquid crystal capsules.

6 In order to make the color of the ink obvious, the black color or other dark color should be selected for the background color. The background color can be water-soluble ink or organic solvent type ink. The printing background can be offset, gravure or silk screen. The organic solvent ink is used to print the background color. After printing, it must be fully dried. The organic solvent must not remain in the ink film. Otherwise, it will react with the liquid crystal and affect the color effect. The scraper hardness is suitable for a Shore hardness of 60-70, a squeegee angle of 60°-70°, and a mesh distance of 4-5 mm.

7 The printing ink layer should be smooth and the thickness of the ink layer should be controlled between 20 and 30 μm. The uneven or too thin ink layer will reduce the color rendering effect.

8 printing sequence. The background color can be printed with black or dark ink first, and then the desired pattern can be printed with liquid crystal ink. The liquid ink can also be used first to fill the bottom, and then the water-soluble black or dark ink can be used to print the desired negative pattern to cover part of the liquid crystal ink.

9 It is best to use a natural drying method. It can also be dried with warm air of about 40°C. It cannot be heated rapidly with high temperature. Do not overlap stacking after drying. Local pressure should also be avoided when breaking.

10 In order to improve the surface abrasion resistance, temperature resistance, gas barrier and maintain the gloss of the ink layer, the surface can be coated with varnish or plastic film.

Second, photochromic ink screen printing process

1. Light change ink

When the substance is irradiated with light of a certain wavelength, the chemical structure will change, the absorption spectrum of visible light will change, and thus the color will change. Moreover, under the irradiation or heating of light of another wavelength, the original color will be restored or not restored. We call this phenomenon of reversible or irreversible coloration and achromatization as "photochromism."

(1) Interference type light change ink

Interference light-change ink is the leader of modern anti-counterfeiting inks. It is a reflective ink with pearlescent and metallic effects, and color copying machines and electronic scanners cannot be copied. For products printed with light-variable inks, ink color patches can be presented in pairs, such as magenta-blue, green-blue, and cyan-green. When the ink blot is tilted to 60°, the pattern can be converted from one color to another. Since only the ink film on the print is thicker, significant color drift may occur, and therefore the print ink layer is required to be thick enough.

Photo-variable ink is a technical product with simple principle and complicated manufacturing process. It adopts an interference film whose coating color changes with viewing angle, and selectively absorbs and reflects natural light (multi-color light) to achieve anti-counterfeiting purposes.

The anti-falsification of light-variable ink is specifically reflected in:

1 The difficulty in the manufacture of light-varying inks lies in the fact that the thickness of the interference film at each layer is difficult to control, and multilayer high-refractive-index dielectric films are required.

2 Film transfer and stripping technology is difficult to control. It is necessary to place the film-coated multilayer composite film in a specific solvent and peel the multilayer film to form fine fragments. The ratio of the top and bottom surface area to the side area of ​​the film is at least 3:1, and then dried in vacuum to make a light-variable pigment.

The optically variable ink can be made by adding these multi-layered film fragments to specially designed binders and adding transparent dyes and other fillers.

Yunnan Hongta Group and Hunan Changde Cigarette Factory launched a new type of anti-counterfeiting cigarette package printed with light-variable ink. When the package is faced with sunlight and viewed from the side in sunlight, the color blocks are green purple and red. Two pairs of color changes are refreshing. This kind of anti-counterfeiting cigarette packaging mainly adopts a new type of optical color-shifting ink produced by Guangdong Huizhou Huasun Sunshine Technology Co., Ltd. in the printing process to achieve a special anti-counterfeiting effect. As this anti-counterfeiting technology of optical color ink is more popular than other general anti-counterfeiting technologies, it has a wide application area, no need for any equipment identification, convenient printing, and strong concealment, and is therefore favored by cigarette factories.

(2) Fluorescence and fluorescent pigment materials are subject to some form of energy stimulation, and the phenomenon of converting the absorbed energy into visible light other than thermal radiation is called generalized fluorescence; the light that still emits intermittent light after isolation is called A narrow sense of fluorescence; the phenomenon of persistent light after stopping stimulation is called phosphorescence.

The main components of fluorescent inks are fluorescent pigments. The difference between these pigments and common pigments is that they can absorb certain forms of energy when they are exposed to external light (including ultraviolet light) and do not convert into heat energy, but they excite photons with low visible light. The form releases the absorbed energy, resulting in a different hue of fluorescence. Different shades of light combine to form an unusually bright color, and when the light is illuminated, the luminescence disappears. The fluorescent ink can be made by mixing and grinding a fluorescent pigment, a polymeric resin binder, a solvent and an auxiliary agent.

According to the molecular structure, fluorescent pigments can be divided into inorganic fluorescent pigments and organic fluorescent pigments.

1 Organic fluorescent pigments, also known as daylight fluorescent pigments. This fluorescent pigment is made of a fluorescent dye (phosphor) that is sufficiently dispersed in a transparent, brittle resin and the color is determined by the dye molecules. When sunlight strikes, it emits a high-brightness visible light other than the normal color because its amount of reflected light increases, absorbing ultraviolet rays that cannot be seen by the naked eye in the sunlight, and converting the short-wave ultraviolet light into a visible long wave. The more ultraviolet light content, the stronger the emitted fluorescence. By blending with or blending with a suitable amount of non-fluorescent pigments, a variety of different color tone fluorescent pigments can be obtained. If there is no UV radiation, the pigment is a general shade pigment that is not fluorescent.

2 inorganic fluorescent pigments, also known as ultraviolet fluorescent pigments. This kind of fluorescent pigment is made of metal (zinc, chromium) sulfide or rare earth oxide and trace active agent. It is calcined and is colorless or pale white. Only under the irradiation of ultraviolet light, depending on the type and content of the metal and the activator in the pigment, spectra of various colors are exhibited.

2. Fluorescent ink screen printing process

(1) General fluorescent ink screen printing process

The screen printing fluorescent ink is an ink made from a fluorescent pigment as a color material. Fluorescent pigments are formulated with fluorescent dyes and synthetic resins. The pigment size is 5-15 μm.

Screen printing fluorescent ink is suitable for the printing of paper and vinyl film. There are two types of paper-based fluorescent inks: oxidative drying and volatilization, and fluorescent inks for vinyl films are volatile drying. When using fluorescent inks, note the following points:

1 Since the fluorescent ink has poor light resistance, it is not suitable for long-term outdoor use.

2 Fluorescent inks are suitable for printing with screens up to 200 mesh/inch, high-tension screens, and neutral hardness squeegees.

3 When the ink transfer amount on the substrate is 50-60g/m2, the hair color and light resistance are ideal.

4 The paper with higher whiteness should be used. When the substrate is transparent, white ink should be printed first, which can improve the fluorescence effect.

5 fluorescent inks should not be mixed with other inks.

6 If the yellow and magenta versions of multi-color printing are printed with fluorescent ink, bright screen printing products can be obtained.

7 For the base color, if the same color system is used for printing, the ink concentration can be high and the light resistance can be improved.

8 Drier is the cause of discoloration and should be used as little as possible.

9 pay attention to the printing order to improve the printing effect.

10 gloss processing will slightly reduce the fluorescence effect, it should use high transparency of light oil.

(2) UV fluorescent ink screen printing process

This ink is milky under sunlight and general lighting. After being exposed to ultraviolet light, it can show a distinct fluorescent color. The luminescent properties of commonly used inorganic phosphors are shown in Table 1. Compared with general fluorescent inks, UV fluorescent inks have the advantages of heat resistance, solvent resistance, light resistance, and drug resistance.