Screen printing ink promotion and application

Screen printing is a printing method capable of printing on all materials and substrates with different shapes except air and water, and the printing ink layer thickness can reach 60 micrometers, which is 4 times the thickness of the gravure ink layer. Ink printing has always played an important role in screen printing. It not only determines the quality of screen printing products, but also affects the screen printing speed. However, there are many kinds of screen printing inks, and the ink system is very complicated, and there is a common problem that the ink is cured and dried. Ultraviolet light radiation curing inks and electron beam curing inks have become two types of inks with great market development potential in screen printing inks.

China's screen printing industry started late. The development and application of modern screen printing technology began in the early 1980s. After entering the 1990s, with the growth of the industrial economy, the screen printing industry has developed accordingly. According to the survey, the annual average consumption of ink by the screen printing factory is approximately 782 kg. The total annual consumption of screen printing ink in the country is more than 20,000 tons (including fabric printing paste), of which about 55% are imported screen printing inks. This is because: First, domestic inks have few varieties, and their output is low, and they cannot meet user requirements; Second, the quality of some high-end domestic inks is still not stable. My domestic development of screen printing ink manufacturing industry can be said to be from scratch, from small to large. Currently, there are more than 50 manufacturers producing screen printing inks in the Mainland, producing more than 130 kinds of products (including special screen printing inks such as silk printing pastes, luminous, fluorescent, reflective, etc.). The annual output of screen printing inks is more than 8,000 tons, and the output value is 240 million. Yuan around. With the expansion of the application of screen printing technology in the industrial sector, the production of screen printing inks in China has also achieved certain development. Currently, there are both solvent-based inks suitable for various substrates, and newly developed screen-printed water-based inks and ultraviolet light. Cured ink.

At present, the world's screen printing inks are moving in the direction of quick-drying, non-toxic and non-polluting. Of course, the development of screen printing inks depends on the expansion of screen printing applications. Now the application of screen printing technology has expanded into the printing field of packaging and decoration industry, advertising industry and building materials industry. This requires screen printing inks must adapt to the development of screen printing to large-scale, multi-color and combined printing. For example, screen printing can be combined with offset printing, gravure printing, or flexographic printing to form a filament printing machine (ie offset-screen printing combination printing machine) or a flexible printing machine (ie flexo printing-silk-screen printing combination printing machine) due to adhesive silk screen or soft silk printing. Machine production, it requires screen printing ink has a certain drying speed. In addition, the combined printing method is currently used for package printing, so there are three kinds of “green” inks that require non-toxic, odorless, and non-polluting inks to meet the requirements for screen printing development. One is screen printing water-based inks. The other two are UV curable inks and electron beam radiation curable inks.

Screen printing water-based ink, also known as screen printing water-based ink, English name is water base screen printing ink. As its name suggests, water-based inks are water-based ink systems. Compared with solvent-based inks, it is solvent-free, non-toxic, odorless, non-polluting, and environmentally friendly. At present, solvent-based printing inks contain 50% to 60% of volatile components. If the diluent required for formulating ink viscosity is also taken into account, the volatile components emitted by the ink will be released when the printed product is dried. The total content is 70% to 80%. The volatilization of these organic solvents will have an adverse effect on the environment, and it will also have a detrimental effect on human health. There is no doubt that screen-printed water-based inks will be greatly developed and continuously promoted.

First, screen printing water-based ink

The water-based ink binder is composed of an aqueous gum or semi-gel solvent and an emulsion. The acrylates and copolymers are dissolved in water in an exact ratio, and after adding other solvents, a stable binder is obtained. Adding such a binder to pigments and auxiliary materials can produce screen-printed water-based inks. The particles of the composition have such a characteristic that the moisture can be volatilized and released relatively quickly during the formation of the ink layer film, thus forming a dry ink film. The viscosity of the screen printing water-base ink can be adjusted with water during printing, and the used screen can be washed with water. The ink residue remaining on the screen can be removed by a cleaning machine and recycled. However, the use of water-based inks requires that the screen printing plate must have water resistance, so it is necessary to use water-resistant photosensitive adhesive for plate making.

As mentioned previously, the screen printing water based ink contains particles of the composition in the ink, and when the water is volatilized and released relatively quickly, the surface of the ink film can be rapidly dried. Therefore, at 20 °C ~ 22 °C standard room temperature and 5% ~ 60% relative humidity, it is best to use hot air to promote the water to accelerate the volatilization, especially non-absorbing substrates. Soft or rigid polyvinyl chloride and foil coated with adhesive shall be continuous drying devices. The convective air temperature at the inlet shall be maintained at 70°C～80°C, so that the drying temperature of the printed input of the stack can be maintained. Close to 35°C to 40°C. For different materials, the stack drying temperature should be adjusted accordingly to obtain better ink adhesion than solvent inks. In addition, another measure to improve the drying performance of screen-printing water-based inks is to add a small amount of cross-linking agent to improve the anti-diluent, alkali-resistance, and acid-resistance properties of the aqueous system prior to printing.

Second, electron beam curing ink

Electron beam curing ink, like UV ink, is one of the most promising "green" inks in screen printing. Since the electron beam cured ink is not limited by the ink layer thickness, it is safer to operate than the UV light curable ink.

The Chicago household electrical appliance printing company in the United States has used this kind of ink processing to produce membrane switches. The thick-film screen-printed prints are placed in an electron beam radiation drying device, and the ink is fully dried in a few milliseconds under the irradiation of the electron beam. The gloss of the printed product is good, the film is strong in touch, and it is resistant to friction. The effect is very satisfactory. However, the ink and its radiation drying device are very expensive. At present, there are still difficulties in its promotion, but because it can save drying time, ensure product quality, and do not pollute the environment, it has a promising future.

Third, ultraviolet light solid ink and light solid drying technology is the development trend of screen printing

Screen-printing UV inks are radical photopolymers that undergo very rapid changes due to UV radiation and cause polymerization. This characteristic requires the ink to have a special structure that is compatible with this reaction.

The composition of UV ink and ordinary ink is as follows:

Composition of UV Ink Common Ink Composition Pigment Pigment Prepolymer or Polymer Resin Resin Monomer Dryer Additive Additive

Ultraviolet light-cured inks, although their composition, appearance, and rheological properties are similar to ordinary inks, their components must contain materials that are compatible with UV light curing drying conditions. Unlike pigments, its chemical composition and surface treatment affect the ability of UV radiation and the ink to cure and dry. The ultraviolet transmission spectra of the four pigments used in the European color standard range from 200 to 400 mm. According to the curve analysis of the spectrum, it can be determined that each pigment maintains its fixed spectral range. But only the carbon black pigment is the exception, it absorbs almost all of the UV spectrum. Spectral measurements were performed on dispersion sheets of aqueous pigments with a depth of 10 mm.

As previously described, UV inks consist of binders: prepolymers and monomers, as well as photosensitizers and pigments of a certain composition. A photosensitizer is a compound that can be formed under the influence of ultraviolet rays to form radicals. This compound can initiate polymerization of the initial monomer and the prepolymerized reactive group, and at the same time, the ink is cured and dried. The speed of curing and drying depends on the correct choice of pigments and the choice of photosensitizers that enable the inks to produce the desired photocuring under UV conditions. Unlike solvent-based inks, the use of UV-curing dried inks does not lose the fine-grainedness of printed images due to drying. Because the ink is not irradiated with ultraviolet rays, it is uniformly stable and has no drying characteristics. When the printed product passes through the ultraviolet irradiating device for about 1 to 2 seconds, the ink is cured and dried, and the printed product can be directly stacked together. When the UV ink is cured, there is actually no loss of ink, and the resulting ink film is much thicker than the solvent ink. When the solvent ink is dried, it is volatilized through the solvent and the ink film thickness is lost by about 60%. At present, the UV ink curing and drying device stack is too thick for the ink layer to transmit, and the ink layer can only be surface-cured, so the impression ink has adhesion and durability to the substrate.

The use of screen printing UV ink has achieved good printability and print quality so far. 1 Stability: UV inks cure and dry only when they receive UV radiation. It does not crust in the air. Therefore, it is absolutely stable on the screen plate, which is in full compliance with the screen printing requirements. 2 gloss problem: UV ink under ultraviolet radiation can instantly dry the ink layer, so compared with the traditional ink, without relying on the nature of the substrate can get better ink gloss. Compared with conventional inks, better ink luster can be obtained without relying on the printing material to obtain the constellation. When using conventional inks, what happens most often is: After drying, the ink gloss appears to be reduced, but this phenomenon has been eliminated when UV inks are used. 3 Abrasion resistance and chemical resistance properties: The three-dimensional photocrosslinker produced by the photopolymerization of the ultraviolet-responsive ink result unit promotes the ink to have the abrasion resistance required by the composite professional, as well as resistance to acids, alkalis, and chemicals. performance. UV prints In any case, no need to add printing oil. 4 screen cleaning and ozone problems: UV ink to use different screen cleaning agent and ordinary ink, its composition has outstanding solubility of UV ink, but will not produce erosion of screen printing film and squeegee. The ozone produced by the UV ink during the drying process is an allotrope of oxygen, which is caused by UV radiation with a wavelength of 220 mm or less. The generated ozone can be discharged to the outside by the exhaust fan of the cooling lamp. In the air, ozone is immediately decomposed into oxygen. When mass-produced, the ozone level per cubic meter of air around the machine will not exceed 0.1 mg. This content is combined with the permitted ozone content around the working environment as defined today. 5 Printing quality: Ink does not occur in the printing process. Ink penetration changes the color tone of printed products. Because no solvent volatilizes, it can be printed on poorly absorbent substrates with good adhesion. The photocured and dried ink film has a good handle quality, and the ink taste is extremely small.

In summary, due to the characteristics of screen printing UV inks with low solvent content and no pollution to the environment, “green” inks have attracted increasing attention from the screen printing industry in various countries in the world in recent years, and have invested a lot of manpower and material resources one after another. Develop research and production of UV inks.

Source of information: pack.cn