Offset printing ink (below)

2, the composition of UV offset ink

(1) Photosensitive resins, also known as oligomers, are oligomers with unsaturated groups at the end of the molecule. They are the main film-forming material for inks, accounting for approximately 30% to 50%. The most commonly used photosensitive resins are epoxy acrylates, urethane acrylates, polyester acrylates, polyether acrylates, various types of modified acrylates, and the like. Their performance largely determines the physical properties, chemical properties, printability, and print performance of the ink. The largest amount of epoxy acrylates is used, which is characterized by good wettability of pigments, strong adhesion, good compatibility with other resins, fast photocuring rate, high hardness, high gloss and resistance to smear after curing. Injury, heat resistance and chemical resistance are excellent. Urethane acrylates have a wide range of applications. They are characterized by better ink film toughness than epoxy acrylates after curing, but some have poor weather resistance. The photosensitive resin used in different uses of ink is not the same, according to the ink required performance to choose, use alone or with several resins.
(2) Reactive Diluent This is a type of reactive monomeric compound that is initiated by photoinitiator polymerization to form an ink film. The main feature is an unsaturated monofunctional or polyfunctional monofunctional acrylate at the end of the molecule. Its main role is to adjust the viscosity of the ink for easy printing. In the ink accounted for 40% - 60%. Reactive diluents also have a great influence on the ink properties. In the selection, the diluting effect, curing speed, ink film adhesion, ink film hardness and other properties should be taken into account. Usually several diluents work better together.
(3) Photoinitiator Photoinitiator is a compound that is easily excited by ultraviolet light to generate free radicals or cations. Although the content in the ink is small (usually 1% to 5%), the effect on the photocuring properties of the ink is direct and critical. Its role is to absorb ultraviolet light energy, the photolysis reaction occurs to generate free radicals or cations, and then initiate photopolymerization of photosensitive resin and reactive monomers, so that the ink curing film.
(4) Pigment Pigment In addition to coloration in UV offset printing inks, it also has a major influence on various properties of the ink system, such as flowability, storage stability, drying, demulsification, and the like. Because the UV offset ink binder is generally composed of a more polar photosensitive resin and polar monomers. The presence of these polar substances requires that the pigment used in the UV ink be polar, otherwise it will directly affect the dispersibility of the pigment.
(5) Additives are very important for UV offset inks. If no additives are available, the printability of UV offset inks is difficult to guarantee. The commonly used additives are:

a The main role of the dispersant can shorten the wetting and dispersing time of the pigment in the binder and reduce the humidity during grinding.
b Stabilizers UV offset inks are sensitive to both light and heat. Excessive amounts of received light and heat can cause the ink to emulsify and become ineffective. Therefore, thermal stabilizers and light stabilizers are generally added to finished inks.
c Anti-Emulsifying Additives Since the binders used in UV offset inks all have strong polarity, coupled with the low molecular weight of the resins, the anti-emulsification performance of ink systems is generally worse than ordinary offset inks. If an appropriate amount of anti-emulsion aid is added to the UV offset ink, the anti-emulsification performance of the system can be improved.
There are other additives that are used less often.

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With the development of printing technology, UV offset printing technology will be popularized, UV offset printing ink is used more widely, so what problems should be paid attention to when selecting UV offset printing ink?
(1) Note that the transmittance of UV inks is magenta, yellow, cyan, and black, respectively.
(2) Choose a UV offset ink that is compatible with the substrate.
(3) In principle, UV inks can be used without adjustment, but depending on the circumstances, 2% to 5% of UV-specific varnish or detackifier can be added.
(4) The auxiliary or cleaning agent for UV ink should be used.
(5) Do not mix with oily inks. If it is necessary to mix with other types of inks, the fluidity, adhesion, printability, and degree of gelation of the mixed ink must be confirmed beforehand.
(6) Fluidity deterioration occurs when UV gold silver ink is mixed with other UV inks. The gelation speed is faster and the gloss is poorer. Therefore, the mixed ink should be used immediately. Do not store it for a long time.
(7) UV inks should be kept in a dark place below 20°, especially UV gold and silver inks. They are hard to cure and cannot be stored for a long time.

(4) Pearlescent ink

Offset pearlescent ink is a part of the lithographic special ink. Its print has delicate pearlescent luster and strong light refractive index, which can improve the grade of printed matter, mainly used for printing high-end packaging, trademarks and pictures.

Offset pearlescent ink consists of pearlescent pigments, binders and additives and other substances, and has a certain degree of fluidity of the paste adhesive, after mixing and mixing evenly, after drying on the substrate can show a soft pearl effect.

1. Pearlescent Pigment Pearlescent pigment is a new pigment that is neither soluble in water nor soluble in linking materials. This pigment can reproduce the pearl luster possessed by pearls and shells. At present, the most common pearlescent pigment is composed of anatase or rutile titanium dioxide coated mica flakes, which can display a variety of delicate, soft silver white luster. This elegant and generous color is more and more popular and accepted by people. Pearlescent pigments account for about 20% to 50% of pearlescent inks.

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It should be particularly pointed out that due to the characteristics of pearlescent pigments, pigments are not allowed to be ground like ordinary inks during the dispersion process, otherwise they will destroy the structure of pearlescent pigments and affect the luster and pearlescent effect of prints. In other words, do not use the ink press when performing ink mix during printing.

2, the characteristics of offset pearl ink

(1) Vulnerability of Pearlescent Pigments Pearlescent pigments consist of anatase or rutile titanium dioxide coated mica flakes, which are very fragile and very easy to break and affect the pearlescent effect.
(2) Fineness of Pearlescent Pigment Offset pearlescent ink has relatively strict requirements on the fineness of the pigment. The particle size of the commonly used titanium pearlescent mica pigment is below 25um. If the pigment particles are too coarse, the transferability of the pearlescent ink is poor, but if the pigment particles are too fine, the pearlescent effect of the print will be less pronounced.
(3) Transparency of offset printing pearl ink The pearlescent effect of offset printing pearl ink depends on the refraction and interference of incident light. Therefore, the transparency of the offset pearlescent ink has a great influence on the pearlescent effect. If the transparency of the ink layer is poor, the original sufficient light will be absorbed and affect the pearlescent effect. Therefore, when selecting the ink binder and the filler, it is necessary to select a material with good transparency.
(4) Viscosity and fluidity of offset pearlescent inks The specificity of offset pearlescent ink pigments requires that the ink be less viscous and more fluid than other common inks, so that it can meet the floating requirements of pearlescent pigments during printing and thus achieve an ideal Pearl effect.

3, offset pearl ink printing should pay special attention

(1) Unsuitable for halftone printing Since the pearlescent ink pigment used is a sheet of anatase or rutile titanium dioxide coated mica flakes, the pearlescent pigments need to be arranged in order before the printed matter can achieve a satisfactory pearlescent effect. The mesh printing is not conducive to the orderly arrangement of the pigments, so the pearlescent ink is more suitable for the printing of solid color patches.
(2) Printing of Viscous Dyed Pearlescent Printing Ink printing is particularly prone to dullness in printing. This is because the offset printing pearlescent ink is less viscous, more fluid, and has larger particles of pearlescent pigments. It is mostly used for printing in the field and uses a large amount of ink. It is generally 2 to 3 times that of normal offset ink. The printing ink layer is relatively thick and prone to stickiness. Therefore, it is necessary to spray dust properly and control the proper stacking height.
(3) Drying speed The printing ink layer of Pearlescent ink is relatively thick. The drying speed of ink is slower than ordinary offset printing ink. At this time, it is not possible to adjust the method of adding desiccant, but it is necessary to control the temperature and humidity of the paper and the printing environment. The ambient temperature should be controlled at 25±2°C, and the relative humidity should be controlled at about 55%.

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Because the offset pearlescent ink is relatively soft, it is easy to emulsify during the printing process. Therefore, in the case of not contaminating the plate, the amount of water supply is controlled to a minimum, and the ph value of the wetting liquid is adjusted to about 5 or so.

Five-web offset printing ink

The ink used in the web offset press is usually called the offset rotary ink. The ink is basically divided into the following two types:

1. Osmosis drying type Because of the high printing speed of web offset printing press and the fast drying speed of ink, the commonly used inks are mostly osmotic drying type. The composition of the ink is basically the same as that of a sheet-fed offset press, but the amount of resin added is relatively reduced, and the content of aliphatic hydrocarbon solvent is relatively high. The rheological properties should be adapted to the requirements of high-speed printing, so the flowability is good. In order to prevent the paper from fluffing, its tackiness should be relatively low to improve the ink transfer performance. In addition, this kind of ink cannot put a desiccant.
2. Thermosetting ink In the second half of the printing apparatus of modern web offset printing presses, a drying device is added. In order to meet the production conditions, the ink has a thermosetting ink. The ink is heated in the drying device and the solvent in the ink is volatilized. The ink film can be dried quickly. The content of dry oil (such as linseed oil) in the thermosetting ink is less, while the content of the petroleum agent is more. The other components are the same as the offset ink of the sheet-fed offset press. The paper used for the ink has better quality than the paper used for the infiltration drying ink.

Source: Ke Yin Network