Exploring the technical points of packaging printing inks
The inks used in medicine and food packaging must be guaranteed to be non-toxic and to control harmful microorganisms and easy-to-use oxides, and they must have no odor. If the packaged print is used externally, the ink must also have fade resistance, water resistance, and high temperature resistance. Therefore, the sample printed on the substrate can be placed in the open air before the ink is used, and the fading test can be performed in the sun using a fading meter and a thermometer. The simple method is to place on the platesetter, set the pulse value, and determine the fade level after exposure. In addition, waterproofing, antifreeze and cooking resistance experiments are also required.
Substances, whether plastic or paper products, are important for their adhesion and softness. The ink must not be layered, not peeled off, and it cannot be wiped off under the requirement of "standing without stickiness". Adhesion is most afraid of hand folds, fingernails, hard objects and metal collisions. If the substrate is a type of corrugated paper, the ink requires higher flexibility and rub resistance. For printing such as pharmaceutical foils, it is very important to prevent over-eating and harmful microorganisms from exceeding the standards. Followed by the ink agglomeration, when the printed products are affixed to each other, the agglomeration phenomenon occurs easily. There is also adhesion failure after the ink film softens at high temperatures.
Packaging and printing operators should also consider whether the inks used are suitable for post-printing processes such as heat sealing, water resistance, solvent resistance, and the like. If you can print a series of post-printing decoration after printing, you will not be able to give up.
The color of the ink is very important, and the composition of the pigment plays a crucial role in the color of the ink film. To obtain good color strength when printing, the distribution of the pigment must be uniform. The poor composition of the ink can cause insufficient color, stacking ink, blocking the plate, and accelerating the wear of the plate, so the preparation of the pigment must be measured repeatedly using a crystal fineness meter. The manufacturer of the ink must be measured three times in succession with the squeegee fineness.
In the production of inks, the pigments should be formulated with relatively high-quality raw materials with high quality and close to the requirements of various technical parameters. In order to reduce production costs, some manufacturers use low-cost raw materials to produce inks with lower color. Such inks can also look in containers, but printing ink films can cause a series of troubles. Due to such poor ink hiding power or fading, discoloration, the film must be thickened in use, the same amount of ink can not print the same number of packaging printing products, the final result is to increase the printing cost, so do not Use cheap ink.
The use of inferior or expired inks in lithographic, letterpress, stencil, gravure, or even jet printing is even more important because it ensures that the magenta, cyan (blue), yellow, and black colors exhibit a distinct hue. Before use, you can paint with a color bar or color wheel. It is best to determine the hue of the ink before proofing on the printer. The hiding power of the ink can also be known by scratching or proofing. The three primary colors of packaging printing can be quickly measured using the optical density measurement method with the aid of a color control device. This method is also very helpful for observing whether the printed sheets and the proofs match. It is also possible to monitor whether the colors before and after printed sheets are the same and whether they are overprinted accurately.
In a colored job with a dot, the use of densitometry is very important for observing whether the color meets the requirements of the user. The color of the printed color is different under different lighting conditions. This phenomenon is called conditional color matching. In order to avoid errors, printing operators, ink suppliers, and users should unify observation conditions. The observation of color is a complex theoretical problem, and a good solution can make the printing operator avoid a lot of unnecessary trouble when changing the ink.
It is generally not practical for ink mills to produce specialized (spot color) inks for special colors with a very small range of applications. Because most ink factories can only produce hybrid inks, each ink is accompanied by instructions for use. At present, many color computer observation systems, including mercury pantone systems, can help printers quickly reach their color requirements, and can save a lot of money; the use of spectrophotometers can measure the color under the lens .
In order to maintain a very good printing effect, the packaging printer must also pay attention to its adaptation to conditions such as printing presses, printing plates, drying systems and substrates, and maintain proper viscosity, concentration, adhesion, gloss, and drying conditions. The quality of ink drying depends on its drying speed and equipment conditions. The successful transfer of images depends entirely on the viscosity (stickiness) of the ink, because the ink is ultimately made into a thin ink film, which has been tested several times by an ink tension meter. The more viscous ink is more accurate when printing lines and dots, and is resistant to emulsification. However, the viscosity of the ink is too high, it can easily cause the paper to pull hair, ink film hair, Alice, warping, easy to heap ink, and the lack of printing clear full version of the field. For example, in the packaging printing process, if the surface of the paper has a low degree of force, the printer must use a lower viscosity ink to prevent the substrate from picking up. The tensile strength of the paper can be tested using a Dennison Pole Tester.
It is well known that viscosity also affects wet-press wet-overprinting. The sign of success in the ink transfer is fully reflected in the ink film, so the ink must first have a high viscosity. Moreover, in order to make the printing effect very good, the ink of each color layer should keep its viscosity lower than the ink of the upper layer of oil. The ink transfer effect also depends on the thickness of the ink film. In the past decade, a coupling agent has been introduced into the ink system to increase the density of the ink film to reduce the thickness of the ink film because a relatively thick ink film tends to lift the layer. By increasing the thickness of the ink film and lowering the viscosity layer-by-layer, the printer can improve the wet-wet printing effect. By adjusting the viscosity of the ink, you can print a very good overprint color, and you can avoid a type of failure such as paper damage. Excessively soft ink film will not only cause scratches, but will also appear as dirty prints such as dirty prints, beards, and sticks at high temperatures.
Concentration (also known as consistency) affects ink transfer, penetration, color, and drying. The density of lithographic and letterpress printing inks is very high and is called pasting ink. The flexographic and gravure inks are very low in consistency and are referred to as fluid inks. The concentration changes with temperature, the temperature of the ink increases, and the ink thins accordingly. Therefore, the printer must use the ink to know the temperature coefficient of the ink concentration, that is, the rate of change of concentration for different temperatures. The change in ink concentration at high temperatures tends to be particularly noticeable.
Too much ink can also cause the substrate to pick up, stack ink, and change color. Flexo and gravure printers should pay special attention to controlling the concentration of ink. Flexographic printing requires a low consistency ink, but too low a consistency will cause the ink to flow past the dots and cause halo around the image. The thickness of the flexographic printing ink also affects the pigment concentration, whether manually interrupted or continuous. Therefore, if the flexographic printer wants to keep the ink color consistent, the consistency of the ink must not be changed during the printing process. If the gravure printer can not control the consistency of the ink well, this or that problem will occur. If the consistency is too high, it will reproduce the moiré or white line marks, and increase the wear of the squeegee blade and the roller, in particular, the dirty plate caused by the squeegee blade being not clean.
There are many instruments that can measure and control the consistency of inks. The control of ink consistency avoids many printing failures, and it also makes it unchangeable for color. Therefore, the control of color is directly related to the quality of packaging and printing products.
The method of drying the ink after packaging and printing also determines what type of ink is most suitable for the printer. Most of the inks use the following four drying methods: absorption drying, evaporation drying, oxidative drying, and radiation drying. Ultraviolet absorption drying method is mainly used to absorb the liquid in the ink with the substrate. This method used to use porous paper in the past. In recent years, it has been used in cigarette packs. Paper printing usually uses this kind of drying method.
The evaporation drying method is mainly to evaporate the solvent in the ink, usually by means of a hot air drier. This method is mostly used in wet printing. If the wet ink cannot be evaporated at a low temperature, the package printing operator will have to use an oven or electromagnetic wave and finally dry the wet ink by evaporation.
The oxidative drying method mainly uses the oxygen in the air to cause the ink to undergo a chemical reaction to achieve the purpose of curing, and it is mainly used for the dry printing of a sheet-fed paper product, which is required for printing. In order to achieve the desired drying effect, the operator of offset printing (lithography) is to control the PH value between 4.5 and 5.5 before printing. At the same time, after the printing glazing and gluing, the products must also be required to be compatible with the corresponding ink or reconstituted. The use of thermosetting (including mixed dried drying of air blow) drying methods, mainly using heating and blowing devices (such as drying tunnels) on packaging printing machinery to make inks for pharmaceutical aluminum foil inks or metal packaging sheets or webs for printing rolls Baking under temperature control resulted in cross-linked film formation. Ink curing temperature formula design and resistance to water, heat and other experiments are generally completed in advance.
Using UV (only 4% of the sun's ultraviolet rays) ink and electron beam (EB) ink, under the appropriate light source, light intensity radiation, the printing ink film will quickly dry. Many years of practice have proved that the use of this drying method will not cause blemishes, and packaging and printing operators will no longer need to spray powder to prevent filth and adhesion, and can directly proceed with the next process. This type of ink cannot be used for a certain period of time on a packaging press because it does not dry out, but only uses the proper light source intensity to irradiate it, causing it to undergo electron transitions and solidification. These rapid radiation drying inks save a lot of time for packaging and printing operators. In the past two years, there have been no initiator-based water-based UV inks on the market. Because they do not contain any carcinogens, they are highly favored by printers, and at the same time, they recognize the importance of fast ink film formation.
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