Deployment knowledge of the best water-based ink p

2022-07-26
  • Detail

The so-called printability of ink refers to the performance that the ink is transferred to the surface of the printing object at a certain printing speed on a specific printing machine under a certain printing pressure, and fixed on the surface of the printing object after the printing film is dried to achieve the desired printing effect. It can be seen that the printability of ink includes two aspects: printability and printability. The printability of ink involves the adaptation of ink to the corresponding version, machine speed, printing press and printing object, so as to ensure the smooth transfer of ink from packaging container - ink bucket - ink roller - printing plate - printing object; The printing quality suitability of ink refers to the fixation, drying speed, color, gloss, fastness, resistance and other properties that ensure the printing effect of the ink film transferred to the surface of the printing object. Generally, the color effect expressed by ink is called inkiness. The allocation of ink printability is mainly to solve the optimal matching between ink color, ink property and printing effect. Due to the particularity of ink structure, printing plate type, printing object, and use of printed matter, the problem that ink color and ink property do not adapt to printing operation and printing quality is more prominent in the actual use of water-based ink. This paper discusses the deployment principle and method of water-based ink printability

I. structure and properties of water-based inks

water based inks are composed of water-based composite binders, pigments, fillers and additives. It has the following properties:

1. the water-based ink belongs to an alkaline composite system, with a pH value of 7~9

2. the water-based ink belongs to Newtonian fluid system, with low viscosity and good fluidity. It can be used for about 30 seconds (coating Cup 4)

3. the water-based ink is soluble in water before drying, and the printing film turns into water-insoluble imprint after drying

4. the water-based ink belongs to the comprehensive drying type of penetration, volatilization and chemical conversion

5. water based inks are environmentally friendly because they do not contain VOC

6. water based ink is suitable for flexographic printing, mainly used for printing packaging and decoration products, such as kraft paper bags and corrugated boxes; It can also be used for gravure printing, such as candy paper printing

II. Color allocation of water-based ink - ink color adjustment

color is the most intuitive evaluation index of printing quality, which is determined by the color attribute of ink. When water-based ink is used for solid printing with flexo, the allocation of ink color is one of the key factors for the success of printing. The allocation of ink color is discussed below

1. ink blending method

the key to success or failure of ink blending lies in mastering the correct method. The ink color matching can be carried out according to the following methods:

a analyze the original and determine that the ink color matching of the original is carried out according to the color sample of the original. In order to reduce the blindness of color matching, it is necessary to analyze the color of the original first and decompose the color of the original into the three primary colors of the color material, That is, to judge which three primary colors of the original colors are mixed by subtraction. At present, the method of analyzing the original mainly adopts the combination of instrument color measurement and human eye color comparison. Instrument color measurement uses spectrophotometer, optical densitometer, electronic color spectrometer and other instruments to measure the optical density value or tristimulus value of the original color, so as to obtain the quantitative data characterizing the color; Human eye colorimetry is the qualitative range of three colors required to form the original color according to the original color and experience. Because the instrument color measurement is complex, and the color is not a pure physical phenomenon after all, but a comprehensive reflection of physics and human visual physiology and psychology, that is, the final effect of printing color depends on human visual psychological experience. Therefore, it is more direct and convenient to use visual color comparison in the actual ink color allocation. The instrument color measurement is only used for the standard analysis of color

b base ink is manually adjusted and scraped for color comparison. An ideal three primary color ink (base ink) is prepared according to the results of the original color analysis. Accurately weigh the required amount of base ink (e.g. 10g), pick up a small amount of each base ink with an inking knife and adjust it evenly on the glass plate, visually inspect the ink color and the original color, and adjust it while measuring. When the adjusted ink color is close to the original color, the adjusted ink can be used on the scraping paper for scraping. If it is a ink solid bottom printing brush, it is mainly to compare the colors of the toned and the original color. After repeated and careful work of color matching, scraping and color comparison, Until the toned color is completely consistent with the original color. Then, accurately weigh the amount of the remaining base ink, subtract the remaining amount of the base ink from the initial amount of the said base ink, and this difference can be initially used as the amount of each base ink required for the deployment of the original color. Finally, weigh each base ink with this amount for deployment, scraping and color comparison, and correct that the ink color of the blended ink is consistent with the original color

2. precautions for ink color allocation

in order to quickly and accurately allocate ink color of ink, the following precautions should also be paid attention to:

a standard light source should be selected for color comparison. Generally, fluorescent lamps are mostly used for color comparison with naked eyes. Two 40W fluorescent lamps are covered and observed at about 10cm, or the northern half day light can also be used. This natural light is close to the C light source specified by CIE, and the color temperature is 6500k

b the scraping paper shall be the same as the printing object as far as possible, just as the brightness, hue and saturation of the same ink scraping on corrugated yellow board and corrugated coated white board are different

c when tinting, pay attention to the main color deviation. Red is blue (purple) and yellow (golden red), yellow is blue (light yellow) and red (orange red), and blue is red (purple) and green. The main color deviation is usually called color head, which accounts for a small component, but has a serious impact on the result of ink color matching. The color head part also participates in color subtraction mixing, For example, the green brightness of blue head yellow ink mixed with red head blue is reduced with dirty color because the red head of blue ink is mixed with equivalent yellow and blue to produce black components

d in color matching, attention should be paid to the skills of color brightness and saturation adjustment. The adjustment of color brightness and saturation is realized through the correct use of achromatic ink, i.e. white ink and black ink. White ink in color ink can increase the brightness, black ink can reduce the brightness and darken, and white ink in color ink can reduce the saturation and fade

e the color comparison must be carried out after the ink film is completely dried

f the base ink used for color matching must be dispersed to the standard fineness. If the pigment and filler particles in the ink are too large, the saturation and brightness of the ink will be weakened. Generally, the fineness of ink used for flexo is required to be 20 μ M or less

III. formulation of inkability of water-based ink inkability

1. formulation of printing operation adaptability

operational adaptability of water-based ink refers to the adaptability of water-based ink in a series of transfer processes of ink bucket, ink pump, ink roller, printing plate and printing object under certain printing pressure. This property is mainly determined by the rheological behavior of water-based ink. The workability of water-based ink is to adjust its rheological properties, so that the ink has rheological behavior corresponding to the printing conditions in the printing transmission process, so as to ensure the smooth progress of the printing operation

a viscosity and its blending viscosity are the main performance indicators to characterize the suitability of ink printing. The viscosity of ink is lower than other inks. The viscosity of ink is too large or too small, which is not conducive to the printing operation, and even affects the printing quality. Excessive viscosity will cause poor ink transmission, poor transfer, biting, pasting and peeling of printing materials; Too low viscosity will lead to poor ink stability, easy foaming in the transmission process, and printing products are prone to pinholes, weakness, halos, water marks, chalking, ash falling and other faults. During the use of ink, if the viscosity is too large, 5%~15% mixed solvent can be used for mixing. This solvent is composed of water: ethanol =7:3. Do not use excessive tap water for mixing during the adjustment, otherwise it may cause poor dryness; If the viscosity is too small, you can use new ink with the same material performance and higher viscosity for blending

b viscosity and its blending viscosity are the performance indicators of ink resistance to ink film separation in the transfer process. The water-based ink is thin and low viscosity, and the viscosity is usually ignored. In fact, the poor viscosity will also cause the poor adaptability of the printing operation, further affecting the printing quality. When printing on corrugated paper with too large viscosity, there may be problems such as rough drawing, blocking, uneven imprinting, and no light after drying. This phenomenon is more obvious in acrylic water-based ink when the molecular weight of acrylic resin is too large, The solution is that graphene is probably just the beginning of 2D material research when using water-based adhesive remover

c fluidity and its blending fluidity are comprehensive characteristics related to the viscosity, viscosity and consistency of ink, which are affected by the characteristics of water-based binders, the structure of pigments and fillers, and the content of solid components in the composition of ink. If the fluidity of water-based ink is too high, there will be such faults as pattern expansion, unclear level, insufficient ink color, and unclear color. This fault can be adjusted by changing the formula during ink design, and new ink with low fluidity can be adjusted or replaced during ink use; If the fluidity is too small, there will be poor ink transfer, uneven ink discharge, and inconsistent ink color (first deep and then light or first light and then deep). This phenomenon can be adjusted by mixing the diluent (aqueous binder: ethanol ∶ water =2:3:5)

d foam and its elimination water-based ink is low viscosity, thin and liquid. In the printing process, ink pump is often used to supply ink circularly. Air will inevitably mix into the flowing ink, and bubbles of air in liquid will be formed due to the large surface tension of the ink. Blistering affects the normal operation of ink printing, and in serious cases, it will make the printing impossible. The way to eliminate foam is to add 0.3%~0.5% antifoaming agent, such as tributyl phosphate and 080, which are commonly used in ink; On the other hand, the chance of contact between ink and air shall be reduced as much as possible. For example, under the condition of continuous ink supply, the circulation amount of the ink pump shall be reduced as much as possible, and the leakage free ink suction pipe shall be used to ensure that the nozzle of the ink pipe is 30cm below the liquid level of the ink bucket

e stability and the stability of the prepared water-based ink refer to the continuous uniformity of the ink during storage or use. Because the water-based ink is a thin, low viscosity liquid, it often has the phenomenon of pigment, filler and binder delamination, which makes the stability of the ink worse. It is thin up and thick down in the storage container, and the ink color is uneven in the printing process. This phenomenon may be caused by unreasonable formula design, low viscosity of binder, excessive specific gravity of pigment, poor dispersion and excessive solvent. If so, it can be solved by adjusting the formula design; It may also be that the balance of ink and water is broken due to excessive dilution during use. In this way, new ink can be added to the ink bucket for adjustment. In fact, even the ink with reasonable design will have different levels of stratification in storage, which can be eliminated by short-term stirring

2. deployment of printing quality suitability

the printing quality suitability of water-based ink refers to the dryness of the ink after it is transferred from the printing plate to the surface of the printing object to form a printing film, as well as the comprehensive properties of the color, brightness, wear resistance, abrasion resistance and water durability of the printing film after drying. The allocation of color and luster has been discussed in the allocation of ink color. Here, we mainly discuss other inks related to the suitability of printing quality to stop the working face of the oil pump

a drying of dry water-based ink

Copyright © 2011 JIN SHI