Waterless offset ink

The composition of waterless offset inks is similar to that of ordinary offset inks and consists of pigments, resin binders, solvents and diluents, fillers and auxiliaries.

Pigment

The pigments for waterless offset inks are similar to ordinary offset inks. Basically organic pigments are used in addition to carbon black pigments. For example, yellow pigments such as benzidine yellow (PY-12, PY-13, PY-14, PY-83, etc.) are used. The red pigments are Lithol Red (PR-49:1), 6B Magenta (PR57:1), Golden Red C (PR-53:1), 2B Permanent Red (PR-48:1), Blue Pigments Phthalocyanine blue (PB-15:1), green pigments such as phthalocyanine. The amount of pigment used accounts for 15% to 25% of the total amount of ink.

2. Resin binder

The main resin used is similar to ordinary offset printing inks in major categories, and the resin used in waterless offset printing inks mainly consists of rosin-modified phenolic resin, gelatinized rosin-modified phenolic resin, and vegetable oil-modified alkyd resin such as linseed oil. , But since there is no evaporation of fountain solution during the waterless offset process to cool the ink, the sensitivity of the printing process to the temperature is relatively high (this has been improved by the mechanical device), and thus the resin that makes up the ink has a special rheology. The performance requirements, especially the viscoelastic effects of the resin binder, should be given more attention. Generally, the viscoelasticity is higher than that of normal offset printing inks, but the properties of inks are slightly softer. The two are contradictory, but trying to find a suitable balance is the focus of ink formulations. In addition, the resin binder material must have a suitable high cohesion material so that the ink can be completely and cleanly removed and transferred from the printing plate and the blanket.

The viscoelasticity of the resin component and its molecular weight, the degree of cross-linking and the degree of branching are relatively complex, and generally the molecular weight can be 20,000 to 400,000, the higher the molecular weight and the larger the degree of branching and cross-linking. It will exhibit higher viscoelasticity, but the solubility in vegetable oils and mineral oils will decrease, and the degree of resin absorption in the solvent should also be noted.

The phenols used in the rosin-modified phenolic resins are bisphenol A, tert-butylphenol, octylphenol, nonylphenol, dodecylphenol, and the like, as well as maleic acid modified rosin ester resins.

In recent years, the United States Sun Chemical and Flint Ink have successfully developed water-washable waterless offset printing inks. They have entered industrial trials and trials. They did not disclose the types of resins they used, but the principle of water washable inks. It has been speculated that the saponification of the ink can be washed off from the plate or printing machine. Of course, the introduction of this ingredient can make it unnecessary for the printing plant to use an organic solvent type cleaning agent, but the alkali resistance level of the printed product is bound to decrease.

Ultraviolet (UV) and electron beam (FB) cured waterless offset inks are also under development. Epoxy acrylates, polyester acrylates, urethane acrylates can all be used as the main polymer of the binder.

3. Solvents and thinners

In the printing process of waterless offset printing ink, the clear and complete peeling of ink from the image portion of the printing plate is one of the key factors for obtaining a high quality printing product. Over the years, a gradual consensus has been reached on the mechanism of exfoliation. The theory of the “interface diffusion boundary layer” has been accepted by many researchers. The theory is that the solvent in the ink diffuses into the layout to form a thin liquid film layer, so that the adsorption force of the rubber on the ink is much smaller than the cohesion force of the ink, which facilitates the clean and complete peeling of the ink layer. Then transfer to the blanket and paper. According to this theory, the choice of solvent in the ink is important, and it will contain multiple components (including additives). Earlier patents have reported this, such as adding liquid organopolysiloxane to the ink solvent. Some patents have reported that the addition of non-ionic surfactants with HLB values ​​of 11 to 15 (such as ethers of polyoxyethylene or propanol, diethyldiethylene glycol monoethylhexyl ether, etc.) appears to be very effective. More recent studies have suggested that the use of vegetable oil derivatives such as rapeseed oil esters, oleates, etc. as co-solvents can reduce the viscosity of the ink, increase the viscosity value, and elasticity.

In addition to these functional solvents, mineral oils commonly used in offset printing inks and vegetable oils such as soybean oil and linseed oil are still important diluents.

4. Fillers and Additives

The type of filler is similar to conventional offset inks, and calcium carbonate, calcium strontium white, barium sulfate, etc. are still selected. Auxiliaries include wax-type wear-resistant additives in an amount of 0.5% to 2.0%; desiccants such as cobalt naphthenate, manganese naphthenate, etc. (if necessary, added in the formulation), with an amount of 1% to 3%; and others Special application function additives.

Lithographic offset printing is a more complex printing method. Eliminating fountain solution can improve print quality, improve production efficiency, and be more environmentally friendly, but the development of special waterless offset inks matches the surface properties of the new media, achieving smooth ink The transfer, stripping and transfer, there is still a lot of ink formulation work to do, it is worth us to continue to develop this new area is gradually developing.

Author: Fan Hanqing

Reprinted from: Printing Technology