Printing process inks

Printing process ink

The development trend of pad printing inks is still mainly based on solvent inks, and the use of screen printing inks instead of pad printing inks is also very effective. At present, most ink manufacturers use pad printing inks and screen printing inks. Make a series for production. However, there are also many problems with screen printing inks used in pad printing processes. MARABU pioneered the development of pad printing inks. In contrast, special pad printing inks have faster and more stable drying and better thixotropy. The ink layer of the pad printing process is relatively thin. In order to obtain more striking characters, the purity of the pigment in the ink is higher and the fineness is finer. These are the difficulties in manufacturing pad printing ink.

At present, printing ink In addition MARABU company has a special series, Germany's DUJO's printing ink also began to occupy a certain market. In addition, there are only a few special printing inks, and British COATES inks, which are well-known for the production of screen printing inks, also have a small market share as an alternative to medium and low-grade products. The printing ink market is vast and profitable, attracting the research and development of many domestic enterprises. The domestic ink production has recently developed very rapidly. Among the outstanding ones are Zhongshan Zhongyi Ink Coating Co., Ltd., Hangzhou Kewang Special Ink Co., Ltd., and Shenzhen Beautiful. China Ink Coating Co., Ltd.

UV inks have long been popular in the field of screen printing. The last bastion is that UV pad printing inks cannot be replaced by screen printing inks like solvent inks. UV screen printing ink production process is much simpler, as long as the ink permeability is good, the printing effect is very easy to guarantee, and UV pad printing ink requires the transfer of the printing head to the ink acrylic monomer monomer transferability Well, generally speaking, the pad printing head is made of silicone rubber. The affinity of the silicone rubber and the acrylic monomer monomer is poor, and the transfer efficiency will be affected. On the other hand, the solvent ink must be added with the necessary filler to improve. The trimming and trimming of the imprinting, however, can not add too much of such fillers in the UV pad printing ink. In addition to affecting the curing efficiency, the transparency of the ink will be difficult to guarantee: in the development of UV pad printing ink, to ensure the color of the pigment High concentration but good transparency and good transferability are difficult points. Now these problems have been overcome. MARABU, a professional manufacturer of pad printing inks, has fully brought their TPC series of UV printing inks to market.

The successful development of UV printing inks has solved some problems that have plagued people. For a long time, the glossiness and abrasion resistance of the text on computer keyboards have not met the requirements of customers. The use of UV inks has become the goal pursued by many manufacturers. However, there are many problems in printing UV inks by screen printing. Nowadays, printing is used. The method to complete the transfer of UV ink, it is easy to meet customer requirements. The printing process features pressure from just above the substrate to complete the printing, so the printing process can easily prevent the product from shaking.

Types of pad printing inks One-component inks can be added with thinner to obtain the desired printing viscosity. The drying method is physical evaporation type. Some thermoplastic substrates such as PS, PC, and PVC will undergo slight dissolution. This dissolution will make the ink and the substrate. Direct adhesion occurs, so it is resistant to scratches and adhesion.

The chemical resistance of two-component inks is higher. Generally, hardeners are added to the inks, but care must be taken to add them before printing. If the addition time is too long, the effect is not good. In addition, whether or not it is completely dry depends on the ambient temperature. It takes several days to dry at room temperature at 20°C, so do not perform scratch and adhesion tests prematurely.

Thermosetting inks are generally two-component inks. The resin bonding of such inks does not occur at room temperature and only occurs at high temperatures.

Oxidation type inks react by air oxidation, and the reaction speed is generally slow. It is 1 to 2 days at room temperature.

The transfer of the printing ink mainly relies on the evaporation of the solvent, the evaporation causes the ink film to adhere, and the adhesion of the ink is adjusted. Good hiding power is achieved through the transfer of the ink film layer. Due to the lack of solvents in UV inks, the ink film layer cannot be changed. This shift is "water transfer" and the transfer is difficult.

UV curing inks are generally used for high quality printing. Advantages of UV inks: Ink on steel stencils is not dry; quality is guaranteed; less wear on steel stencils; faster drying speed; solvent-free. The disadvantages of UV inks are: high energy requirements, UV curing equipment; high requirements for cleaning rubber heads; viscosity requirements are not as good as solvent inks; fineness printing is not as good as solvent inks.

Water-based inks have not been used for pad printing because of the low yield, drying speed, viscosity, adhesion, and evaporation rate are not as good as solvent inks.

UV Drying Ink Brings Light to the Development of Intaglio Pad Printing

In gravure pad printing, people are eager to find a way to increase the resolution of print resistance and increase printing productivity and efficiency. UV ink in gravure printing in the end played what role? Which process can it use for gravure pad printing? How is it different from traditional ink?

First, the versatility of gravure pad printing is due to the uniqueness of the printing ink used and the uniqueness of the image transfer method. Unlike screen printing inks and offset printing inks, pad printing inks undergo several rheological states when printed on substrates. Correctly formulated inks should not only have good ink transferability, but also have high print resolution and high print speeds.

From the point of view of the development of pad printing inks, pad printing inks include a series of solvent-based formulations, which also include traditional solvent-based inks that are dried by evaporation and oxidation. However, there has recently been a UV drying ink that has the advantages of rapid drying and high resolution and performance of screen printing inks and offset inks. Today, substrates with convex and concave surfaces, such as three-dimensional metals, glass, and plastics, will become objects of UV-drying inks.

1, UV technology and gravure pad printing

UV drying appeared in the automobile painting industry as early as the 1950s, moved to the screen printing market in the 1960s, and occupied a large market share in screen printing in the 1970s. Currently, UV-dried photopolymers include not only inks but also adhesives, silicon-based release agents, pressure sensitive adhesives, and other coatings.

In pad printing, UV drying ink allows users to obtain fine print images, and the image has the characteristics of fast drying, high abrasion resistance, good pressure resistance, and strong solvent resistance. According to the specific ink instructions, if combined with some advanced equipment, UV technology will be fully utilized. Note: Improvements in the equipment include a high degree of automation, advanced time control in the printing process, an improved tight ink tank design, and an automatic ink cleaning device. With these improvements, UV printing will be most widely used.

2, the rheology of printing ink

Pad printing inks, like solvent inks, have certain requirements for rheology. During the printing process, the ink is applied to the printing plate, excess ink is removed by the doctor blade, and the recessed area on the printing plate is filled with ink. After transferring to the pad, the ink thickens as the solvent evaporates. The rheology has changed and the viscosity of the ink has increased. In contact with the substrate, the ink is separated from the print head and transferred to the surface of the substrate.

3, UV drying ink drying

As mentioned earlier, solvent-based pad printing inks are dried by solvent evaporation. In addition, the epoxy-type ink can be oxidatively cross-linked and cured and dried under heating to obtain a large molecular weight. UV pad printing inks are similar to epoxy inks, but they are not dried under heat but dried under UV energy. In high-intensity UV energy, UV inks can be instantly cross-linked and dried.

When UV energy passes through the ink layer, the photosensitive molecules in the ink will interact with adjacent molecules. These single molecules are called monomers and oligomers. The inter-monomer effect causes linkages that make up the molecular matrix. The entire reaction process takes only a few seconds, and if the ink formulation is accurate, the more pigmented ink will also dry quickly. The dried product has higher resistance and solvent resistance than the oxidation-dried product.

So how to get the most effective UV energy is a mercury lamp under moderate pressure. The energy output of this type of lamp can be through a variety of metallic materials and can output a variety of specific wavelengths.

UV pad printing inks can also be printed on heat-sensitive materials such as ABS, polystyrene and plastics. When printing these materials, it is best to have a dichromatic reflective device as an aid. This device can absorb the infrared light energy and reflect the required UV light energy, which can reduce the temperature of the printing surface and increase the UV light energy. double effect.

4, the comparison of traditional inks and UV inks

If the print job is relatively large, and the solvent resistance and abrasion resistance requirements are high, the use of UV drying pad printing ink is undoubtedly the best choice. In general, UV-drying inks have greater wear resistance than conventional or epoxy inks. The best example is the symbol on each key on the computer keyboard, which are all printed with UV ink. A well-known large company once experimented with using a mechanical “finger” to repeatedly press a keyboard printed with a UV ink and a keyboard printed with a traditional ink. As a result, the keyboard symbol printed on a traditional ink is about 1-2 million times. Worn out. However, the UV ink printed keyboard symbol weared only about 13 million times. The abrasion resistance of UV inks is 1300% of the wear resistance of traditional inks. Not only that, but also the objective drying speed is greatly improved compared to traditional inks, from the original 7 minutes to 15 seconds, saving 96%. time.

UV inks also have extremely high solvent resistance after drying. This solvent resistance results in part from the high crosslink density (macromolecule weight) of the crosslinked dry ink layer. A higher degree of cross-linking allows the use of solvents in conjunction with some solvent-resistant chemicals.

For the purpose of comparison, we look at the situation after replacing the epoxy ink with UV ink. First, do not mix the ink before use. Second, of course, it is time-saving because the epoxy-based ink needs to be dried for a long time under a certain high temperature condition, and the UV ink is almost instantaneously dried. This is accompanied by the additional advantage of reducing the damage of the ink layer caused by heating. UV inks also save a lot of drying workshops.

There is also a drawback to the formulated epoxy ink. Its stability is poor. After mixing for a while, it will condense in the ink fountain. You must stop and wash the ink fountain. This leads to a waste of time and a drop in productivity. However, UV inks are different, and its stability is very good. It can be said that condensation does not occur.

Of course, there are specific factors to consider before converting the ink used. Such as the need to switch to UV ink equipment capital issues, measuring instrument problems. If the surface energy of the surface of the substrate is low, the surface must also be subjected to photochemical treatment to ensure the adsorption of the ink, which requires additional new quality control equipment. It is recommended that you do a good overall planning before the conversion and do not rush. \