In board printing, inks have excellent properties in paper and board printing due to their good performances in abrasion resistance, printability, coating thickness, dot gain, etc., and low content of VOCs (1). Well represented. The following focuses on some of the important factors in ink printing.
Transfer of ink Transfer of ink is often defined as the ability of the substrate to absorb ink. However, this is not very appropriate because it means that the printing paper absorbs a large amount of ink, which may cause excessive consumption of the ink. The use of "ink ink" to express it is more widely accepted and used, this expression may be more accurate. The permeation of the ink is affected by factors such as pressure, the type of ink, the surface smoothness of the paper, and the size of the pores. The absorption of ink by a paper sheet is often effected by a capillary tube. Some acidic papers can speed up the drying of ink by neutralizing the soluble amines in the ink. The principle of ink drying is that the paper absorbs a sufficient amount of liquid components in the ink through osmosis so that the pigment is captured by the resin and fixed on the surface of the paper.
The best effect is that only the least amount of ink that can meet the ink density and quality requirements is transferred and is firmly attached to the paper sheet. Smooth-surfaced papers (such as double coated paperboard and single-coated paperboard) are printed with less ink, while rough-surfaced paper (with lower hiding power) is consumed due to the need to fill the surface with tiny pits. More ink. If you exclude the choice of media type and ink adjustment two factors, the surface roughness of the paper will also produce a higher dot gain value. The extent of dot expansion depends on the type of paper, the surface structure of the paper, and the size of the air holes. Apply ink to the paper. If the ink spreads over the paper surface, it is evident that the dot expansion is significant.
It is very important that the ink is fixed on the surface of the paper and there is no excessive separation between the binder and the colorant. Otherwise, poor wear resistance and chalking of the ink will result. An important aspect of printability is overprinting, where different colors overlap by a given design. Overprinting refers to a layer of ink superimposed on another layer of ink, requiring the first layer of ink to be sufficiently dry before the second layer of ink is overlaid. This requirement is more important for double-sided coated paper and single-sided coated paper than for non-coated paper. It is much easier to obtain a satisfactory overprint on the loose side of uncoated paper. If the coated paper cannot be dried to the best condition after printing, we may consider changing the order of the printing processes.
Temperature effects The control of the drying temperature is critical because the flow properties of the ink depend primarily on the temperature. We must be very careful to keep the temperature stable. An increase in temperature causes a decrease in viscosity. For example, as long as the temperature is increased by a few degrees, the syrup will have near-water-like fluidity from the immobile liquid material. In the printing process, especially a printing process in which a squeegee device is installed and a stable ink transfer amount is required, the performance of the ink after being moderately warmed is significantly better than that before heating. This point of view has been widely recognized in those regions where the temperature control of print shops in North America and Northern Europe is alternately affected by the large fluctuations in seasonal temperatures.
In order to maintain a stable viscosity, it is necessary to control the amount of diluent. The higher the temperature, the less diluent is needed. The thinner of the ink can largely affect the print thickness of the printed product in the actual site. For inks, the release agent can be water or a diluting solvent.
Drying Characteristics and Viscosity Control Factors that affect ink drying on an absorptive surface to achieve adequate drying include evaporation, infiltration, precipitation, and chemical reactions. Evaporative drying is achieved through the action of air and heat. Hot air blows off the volatile substances in the ink when it passes over the surface of the print. Permeation drying is mainly through the action of capillaries, so that the ink is absorbed by the paper surface. Once the ink is absorbed, the print is no longer easily soiled or transferred to the surface of other objects. Precipitation and chemical reactions also contribute to the drying of the ink. Precipitation is the process by which liquid ink is divided into two forms, solid and liquid. The liquid component is absorbed by the paper fibers and the filtered resin and color paste crosslink on the surface of the paper. Chemicals also contribute to the drying of the ink film, but this does not occur in water-based printing of paperboard because the chemical reactions include oxidation, catalysis of the cross-linking reaction, and accelerated drying by ultraviolet, infrared, electron beam, or microwave action. Changes in morphology, etc. The ink is easily dried by evaporation during printing. In order to slow down the evaporation speed of ink on the ink fountain roller and the squeegee device, most modern corrugated paper printers are equipped with a closed inking device.
For printing, a necessary characteristic of the ink is that it should maintain good fluidity before it is transferred to the surface of the substrate. In-process inks usually require the addition of a suitable amount of thinner to dilute the desired viscosity for printing. The vast majority of printer ink tanks are located below the horizontal line of the printing section. The ink is pumped into the ink tank by the ink pump. The ink tank is provided with an overflow tube at a certain relative position to the ink fountain roller so as to maintain a certain amount of ink in the tank. In the process of continuous circulation, the ink is brought into contact with air in the tank and on the drum, which causes some of the solvent to evaporate, which leads to an increase in viscosity, which in turn leads to an increase in the ink concentration. Therefore, the amount of water added to the ink not only affects the viscosity but also affects the ink density of the printed product.
Because inks are particularly sensitive to the addition of thinners, care should be taken when adjusting the viscosity. When adding water, be careful not to overdo it. It is not advisable to add fresh ink to increase the viscosity. Experience has shown that in this case, a large amount of fresh ink is added to achieve the desired viscosity. Therefore, it is the best way to slowly add over-dilution ink to fresh ink. The control of viscosity plays an important role in maintaining ink performance and controlling ink density.
Ink inks have the advantage that they lose only a small amount of solvent through evaporation, so they are adjusted less frequently than solvent inks during the printing process. Since the ink is dried by evaporation during the printing process of paper and board, it is mainly dried by the surface osmosis of the substrate. Therefore, the surface quality of the substrate has become the focus of close attention. The speed of drying depends on the absorptive capacity of the substrate surface and the diffusion of resin or water in the ink formulation. Ultimately, we can find an optimal balance between drying speed and printability. Fast-drying inks for high-speed printing require special care during printing because the inks also dry faster on plates and flower wheels.
Additives The role of additives is to be incorporated into printing inks to improve printing ink properties and obtain certain specialized properties. The actual amount of additives used is generally small, but the types used may be more. In order to make the most effective use of additives, it is necessary to understand their functions, limitations and possible negative effects. Ink can be used for the following types of additives: defoamers, bactericides, waxes, wetting agents, transfer agents, surfactants, coalescents, polymerization inhibitors and smoothing aids. All of these additives can be used to obtain different properties.
Surfactants help pigment dispersion, gloss enhancement and color reproduction of printing inks. Also, it can reduce the probability of flocculation of the colorant after ink dilution. Defoamers are often used when the foam has an adverse effect on ink manufacturing and printing processes, particularly those that require thorough agitation of the ink. If the antifoaming agent is used in excess when it is difficult to eliminate the foam, defects such as uneven printing and shallow pits may occur. In addition, some defoamer products contain hydrocarbons that damage the photo-sensitive polymeric printing plates. If the hardness of the water in the ink is different, the influence of the foam may also be different. Silicon-based antifoams are diluted with water, and the ink is constantly stirred during the addition. If undispersed silicones are used without dilution, pinholes and missed marks may occur. Whenever adding defoamers, special care should be taken. In general, its use does not exceed 1%.
PH Value The change in the pH of the aqueous ink affects the ink supply and the ink density. If the pH is too high, the ink will dry out due to the excess of the amine. Conversely, if the pH is too low, large fluctuations in viscosity may occur. It may even cause the resin in the solution to precipitate. The ink pH test can be easily performed using a standard pH tester. Traditional inks are alkaline and have a pH greater than 7. In general, the ink ink has a normal pH range of 8-9. However, the type of ink formula will affect the adjustment to achieve a moderate pH.
Printing standards To print fine prints, there are some requirements that we need to recognize and meet. These requirements go through the entire process from the design and development of printed products to shipping and shipping. To obtain high quality prints, consider the following criteria:
- the quality of the original;
-- Barcodes can be accurately identified;
——The best screen number standard for multi-color screen printing;
——The quality and type of ink (such as pigment, etc.);
- Water absorption and texture uniformity of the board;
——Ink roller quality specification and squeegee model and adjustment;
- Balance of grayscale;
——Control of viscosity and pH;
- Overprint fastness;
- pressure between printing plate and metal ink roller;
- Printing pressure;
- the assembly of the printing plate (cooperation between printing plate, gasket, tape and bracket);
- equipment assembly;
- The type, thickness and quality of the printing plate;
Optimized printing effects BASF's printing system's nylon flexo FAC-X flexo material and its latest matching inks have already been developed. The combination of the two can achieve a smaller dot gain value, a smoother print output, and fewer defects. Version times and best results in better ink transfer performance. The photosensitive resin plate for corrugated printing uses a new, higher-purity raw material with the best surface properties and an improvement in the manufacturing process. This new printing plate can obtain a uniform and thick ink transfer at a set minimum printing pressure. The amount of ink transferred by the FAC-X plate and its release properties to the ink are determinants of the ink density and the ink coverage performance. Today, some experienced printers will use different series of flexo plates with different types of tapes and pads to achieve the best results.
Sometimes, in order to match with a particular device or cardboard material, it is necessary to make the maximum use of some characteristics of the plate such as elasticity, hardness, and ink transfer ability. Using FAC-X flexographic plates does not require experimentation and matching in this area. For printing plates, the most basic requirement is to produce a uniform, thick, low dot expansion ink transfer. Other common requirements are subtle images and lines such as barcodes
Fine ink printing
December 20 18:08:10, 2023
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