Blending technology of printing suitability of the

2022-08-24
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The blending technology of water-based ink printability

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 printing suitability of ink includes two aspects: the suitability of printing operation and the suitability of printing quality. The printing suitability of ink involves the adaptability 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. Usually, 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 the use of printed matter, the problem that ink color and ink property are incompatible with 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 printing suitability

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. Water based ink belongs to alkaline composite system, with pH value of 7~9

2. 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 can be dissolved in water before drying, and the printing film will turn into water-insoluble imprints after drying

4. water based inks belong to the comprehensive drying type of penetration, volatilization and chemical conversion

5. Because the water-based ink does not contain VOC, it is determined that this kind of ink is environmentally friendly when oil is injected into the upper chamber of cylinder 4

6. Water based ink is suitable for flexographic printing, mainly used for the printing of 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

second, the allocation of water-based ink color - toner

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

1. ink blending method

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

a analyze the original, and determine that the color matching of ink is carried out for the color sample of the original. In order to reduce the blindness of color matching, we must first analyze the color of the original, 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 color are mixed by subtraction. At present, the method of analyzing the original mainly adopts the combination of instrument color measurement and human eye colorimetry. Instrument color measurement is to use 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 more 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 the visual psychological experience of human eyes, so it will be more direct and convenient to use visual color comparison in the actual ink color allocation, and the instrument color measurement is only used for the standard analysis of color

b base ink is manually adjusted, scraped and compared. According to the results of color analysis of the original, an ideal three primary color ink (base ink) is prepared. Accurately weigh the required amount of base ink (such as 10 grams), pick up a little 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 face color of the original. 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, color comparison, and correct the ink color of the blended ink to be consistent with the original color

2. Precautions for ink color allocation

in order to quickly and accurately allocate the ink color of ink, we should also pay attention to the following matters:

a standard light source should be selected for color comparison. Generally, when comparing colors with the naked eye, fluorescent lamps are mostly used, with two 40W fluorescent lamps 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 should be the same as the printing object as much as possible, just as the brightness, hue and saturation of the color of the same ink scraping on corrugated yellow board and corrugated coated white board are different

c when tinting, pay attention to the deviation of the main color. Red is blue (purple), yellow (golden red), yellow is blue (light yellow), red (orange red), and blue is red (purple) and green. The deviation of the main color is usually called the color head, which accounts for a small component base, but it has a serious impact on the result of ink tone matching, and the part of the color head also participates in the subtractive mixing, For example, the decrease of green brightness and dirty color obtained by mixing blue headed yellow ink with red headed blue is due to the black component produced by mixing the red headed part of blue ink with the equivalent yellow and blue

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 achieved through the correct use of achromatic ink, namely white ink and black ink. The brightness can be increased by adding white ink to color ink, the brightness can be reduced and dimmed by adding black ink, and the saturation can be reduced and dimmed by adding white ink to color ink

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 Below M

III. allocation of inkability of water-based ink inkability

1. allocation of printing 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 deployment of water-based ink is to adjust its rheological properties, so that the ink has rheological behavior suitable for 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. The viscosity is too high, resulting in poor ink transmission in the transmission process, poor transfer, printing biting, plate pasting, orange peel and other faults; Too low viscosity will cause 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. In the process of using 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 adjustment, otherwise it may cause poor dryness; If the viscosity is too small, you can use the same kind of new ink with 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 printing operations, which will further affect 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 the acrylic acid water-based ink of the national standard of acrylic electronic universal testing machine when the molecular weight of acrylic resin is too large, The solution is to use water-based adhesive remover appropriately

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 faults such as pattern expansion, unclear level, insufficient ink color, and unclear color. This fault can be adjusted by changing the formula during ink design. In the use of ink, new ink with low fluidity can be adjusted or replaced; If the fluidity is too small, there will be poor ink transmission, uneven ink discharge, and inconsistent ink color (deep before and light after or light before and deep after). 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 pumps are 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 ink. Blistering affects the normal operation of ink printing, and in serious cases, it will make the printing operation impossible. The way to eliminate foam is to add defoamers with a formula amount of 0.3% - 0.5%, such as tributyl phosphate and 080 commonly used in ink; On the other hand, the chance of contact between ink and air should be reduced as much as possible. For example, under the condition of continuous ink supply, the circulation volume of the ink pump should be reduced as much as possible, and the leakage free ink suction pipe should be used to ensure that the mouth of the ink pipe goes deep into 30cm below the liquid level of the ink bucket

e stability and the stability of the water-based ink refers to the continuous uniformity of the ink in the storage or use process. Because the water-based ink is a thin and low viscosity liquid, there is often the phenomenon that the pigment, filler and binder are layered, which makes the stability of the ink worse. It is thin and thick 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 by excessive dilution during use, so new ink can be added to the ink bucket for adjustment. In fact, even the ink with reasonable design will have different degrees of stratification in storage, which can generally be eliminated by short-term stirring

2. allocation 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 lustre has been discussed in the allocation of ink color. Here, we mainly discuss other aspects of inkiness related to the suitability of printing quality

a the drying of dry water-based ink is mainly through water compounding

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