ink, pad print ink

Pad printing ink

Pad printing ink is a special ink for pad printing machines.

Features
• Good transferability: suitable viscosity and surface tension, easy to peel off from the pad printing silicone head, transfer to the surface of the substrate, and ensure the complete transfer of the pattern.

• Rich and stable colors: provide a wide range of color options, and the colors can remain bright and fade-free for a long time after printing, with good light resistance and chemical stability.

Ingredients

• Pigment: determines the color of the ink, and the quality of the pigment affects the hiding power, light resistance and other properties of the ink. For example, the use of high-quality organic pigments can make the printed color bright and long-lasting.

• Binder: mainly plays the role of bonding pigments, and at the same time affects the drying speed, adhesion and other characteristics of the ink. For example, resin binders can make the ink adhere better to the substrate.

• Solvent or diluent: used to adjust the viscosity of the ink to meet the requirements of pad printing. Different solvents also affect the drying method and speed of the ink.

Application areas

• Toy industry: used to print patterns, logos and decorative patterns on the surface of various toys. The facial features of plastic dolls and the logos of toy cars are all printed with pad printing inks.

• Electronics industry: Printing brand logos, models, patterns and other information on the shells of electronic products. For example, mobile phone cases, computer mice and other products, pad printing inks can achieve fine pattern printing.

• Household goods industry: Used for surface printing of household decorations, tableware, stationery and other items. For example, printing exquisite patterns on ceramic vases, or printing trademarks on plastic stationery.

Classification by drying method

• Solvent-based pad printing ink:
Mainly relies on solvent evaporation to dry. The drying speed can be adjusted by adding slow-drying solvents or fast-drying solvents. Generally, pad printing ink dries faster and can be dried naturally or with IR tunnel furnaces.

• UV pad printing ink:
Although the ink layer of pad printing ink is thin, it has strong covering power, so the color concentration of pad printing ink is high, which is bound to affect the penetration of UV light, so UV pad printing ink has been progressing slowly. Through the research of ink engineers, UV pad printing ink is now basically mature and has been maturely applied on ABS materials.
Under ultraviolet light, the photoinitiator in the ink will trigger a polymerization reaction, causing the ink to solidify instantly. Since there is almost no solvent volatilization, the environmental protection performance is good. It is often used for pad printing of high-precision products that need to be produced quickly, such as mobile phone shells, high-end cosmetic bottles, etc.

UV pad printing ink need UV curing unit to dry

Pad printing ink application

The process of pad printing ink transfer is briefly described as follows: first pour the oil pan into the oil pan, and then the ink will be coated on the surface of the printing plate driven by the inking device; the scraper will scrape off the ink coated on the surface of the printing plate, as shown in the figure The ink in the text will remain in the pit; the pad printing head moves to the top of the printing plate to stick the ink in the pit of the printing plate; the pad printing rubber head moves to the substrate to print the ink on the product surface.
The process of pad printing ink filling the pits of the printing plate requires that the pad printing ink has good fluidity and cannot be dried before the pad printing rubber head is dipped; after the ink is dipped by the pad printing head, it must be ensured that the ink has sufficient plasticity, that is, the ink cannot There are changes in form. The transfer of ink on the surface of the rubber head is similar to the release state of the thermal transfer film, which must be completely transferred without major changes.
Pad printing ink requirements:
1. Fast and stable drying. Compared with screen printing ink, the drying speed of pad printing ink is faster. If the drying speed is too slow, the transferability will be affected, but this is relative. If the drying speed is too fast, the ink will dry on the printing plate. deep. In addition, it is very important for the pad printing ink to have a more stable drying speed range. When the ink is brought from the oil pan into the printing plate, transferred to the surface of the rubber head, and printed on the surface of the product, the amount of ink transferred is very small. To ensure the stability of printing suitability, the ink must maintain a stable drying speed, so the purity of the solvent in the pad printing ink should be higher than that of the screen printing ink.
2. The color concentration of pad printing ink is higher. The ink layer of pad printing ink is similar to that of offset printing. In order to obtain brighter colors, the color concentration of the pigment in the ink must be high, but too high a color concentration means that the adhesion will decrease. Obviously, we will have to refine the molecules of the pigment And choose better resin to make up for this deficiency.
3. Pad printing ink has more stable colloidal properties. Ink is a kind of suspension, and it will appear delamination when it is left for a long time. A uniform amount of ink is obtained on the head surface, which is similar to offset printing ink properties.

Marabu Pad printing ink

Although screen printing ink is able to be used by the pad printer. Appropriative pad ink is recommended by the pad printing expert because of steady surface tension and nice ink transfer result. There are three kinds of pad inks in Chinese pad printing market.

1.TPR

This glossy pad printing ink is distinguished by particularly high resistance. Being an one-component ink, it is very quick-drying and easy to be processed. To raise surface stability or other stabilities, hardener can be added. This pad printing ink can be widely used. On rigid PVC, polystyrene, ABS, acrylic glass, polyester, thermosetting plastics and varnished surfaces. Because of its high resistance, it can also be utilized for products subject to high mechanical stress, the effects of hand perspiration or cleaning agents, such as control knobs, camera housings etc. Under certain circumstances, this ink is also suitable for poly-acetal materials.

2.TPU

High-gloss, quick-curing two-component ink for high-demand adhesion, scratch resistance, mechanical and chemical resistance. By using a matte paste, the degree of gloss can be varied. Materials that are difficult to print on, such as pre-treated polyethylene and polypropylene, thermosetting plastics, metals and varnished surfaces, but also polyurethane, polyamide, melamine resins, powder-coated surfaces and suchlike are easily printed. It can also be used for polyacetal under certain circumstances.

3.TPY

Glossy, quick-drying pad printing ink with good resistance to many chemicals such as oils, greases, alcohol. Hardener can be added to further raise surface stability and other properties. Tampapol TPY is primarily used for printing on packaging made of pre-treated polyethylene and polypropylene, ABS as well as rigid PVC. It is also widely used for thermosetting plastics, metals and varnished surfaces.

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Substrates

The UV-curable pad printing ink Tampacure TPC is particularly suited to print onto · ABS · Rigid PVC · Polycarbonate (PC) · Polystyrene (PS) · Acrylic (PMMA) By adding hardener, TPC adheres excellently to many other substrates such as · Pre-treated polyethylene (PE), · Pre-treated polypropylene (PP), · polyamide (PA), · varnished surfaces. When printing onto metals, an addition of Adhesion Modifier UV-HV 1 may improve the adhesion of the ink. In the case of printing onto polyethylene and polypropylene, please make sure to pre-treat the surface of your substrate by flaming or Corona discharge as usual. As per our experience, you can achieve a good adhesion with the Tampacure TPC with a surface tension of at least 48 mN/m. On polypropylene, you can also apply a thin film of our colourless Primer P 2 for surface pre-treatment. Since all the print substrates mentioned may be different in printability even within an individual type, preliminary trials are essential to determine the suitability for the intended use.

The UV-curable Tampacure TPC is particularly suited when printed parts are immediately to be processed further, resp. when excellent mechanical and chemical resistances are required. With multicolour printing, it is important to note that Tampacure TPC can be printed weton- wet, without an intermediate UV-curing. When printing overlapping motives with opaque colour shades, however, the individual ink films must be cured one by one. If the different ink layers do not overlap, it is possible to cure all printed layers with one single pass through the curing unit. Due to their transparency, 4-colour process shades can also be cured with one pass through the curing unit. Nevertheless, preliminary tests are always essential.

UV-Curing

According to the required curing speed, a UVcuring unit (medium-pressure mercury lamps) of 80-120 W/cm is necessary. The curing speed of the ink is generally dependant upon the kind of UV-curing unit

(reflectors), number, age, and power of the UV-lamps, the printed ink film thickness, colour shade, substrate in use, as well as the printing speed. The adhesion of the ink is usually tested by a tape test after the ink has been cooled down to room temperature (approx. 20° C).

Drying

UV Pad Printing ink contains solvents. Parallel to physical drying and the evaporation of the solvents

used, the actual hardening of the ink film is caused by a chemical cross-linking reaction started by the UV-light. UV Pad printing ink is a slightly post-curing UV ink which will achieve its best resistances after 24 hours. If hardener has been added, the curing speed will be reduced. Due to this, adhesion and scratch resistance should be tested only after 24 hours. A final curing of the ink film will be reached after approx. 48 hours.

Pot life

The pot life (processing period) at room temperature (approx. 20°C) with hardener will be about 12-16 h. Higher temperatures reduce pot life. . If the mentioned times are exceeded, the ink's adhesion and resistance may be reduced even if the ink characteristics show no noticeable change.

When using hardener, the processing and curing temperature must not be lower than 15°C as irreversible damage can occur. Please also avoid high humidity for several hours after printing as the hardener is sensitive to humidity.

Fade resistance

Pigments of medium to high fade resistance are used in UV Pad printing ink. Owing to this, all UV Pad printing ink shades are generally suited to a short-term outdoor use of up to one year related to the

moderate Central European climate.

Stress resistance

After proper and thorough drying, the ink film exhibits outstanding rub and scratch resistance

and is resistant to a large number of chemicals, oils, greases, and solvents, as well as perspiration. These resistances can further be improved by adding 5% hardener.

Ink adjustment

UV pad printing ink is not press-ready and must therefore be adjusted to the required viscosity

with the corresponding thinners prior to printing. In the case of higher requirements to the ink’s resistance or reactivity, there are different additives available.