Blending principle of the hottest solvent type pol

The formulation principle of solvent based polyamide plastic gravure printing ink

1 preface

the printability of ink includes two aspects: printability and printing quality. The suitability of printing operation of ink requires that the ink should adapt to the corresponding version, machine speed, printing press and substrate. The suitability of printing quality of ink refers to the fixation, drying, color shown by the ink film transferred to the surface, as well as the gloss, fastness, resistance and other properties that ensure the printing effect after the film is formed. Generally, the aspect of color effect expressed by ink is called ink, and other aspects related to ink printability except ink are called ink. 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, substrate, and use of printing materials, the problems of ink color and ink property incompatible with printing operation and printing quality are more prominent in the actual use of plastic gravure printing ink, and the ink mixing task is relatively heavy. According to the author's experience in ink design and application guidance, This paper discusses the mixing principle and method of the printability of the commonly used solvent based polyamide plastic gravure ink

2 toner

2.1 ink blending method

(1) analyze the original and determine the color. The effective integration of production, study and research resources of plastic concave ink color matching is aimed at the color samples of the original. In order to reduce the blindness of color matching, we must first analyze the color of the original, that is, judge the proportion of the three primary colors of the original. At present, the method of analyzing the original mainly adopts the combination of instrument color measurement and visual colorimetry. 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; Visual colorimetry is the qualitative range of the three primary colors required to form the original color according to the combination of 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

(2) base ink manual adjustment, scraping and color comparison. According to the results of the color analysis of the original, prepare an ideal three primary color ink (base ink). According to the actual experience of ink mixing, the plastic concave base ink should include base ink black and white in addition to red, yellow and blue. When mixing colors, first of all, accurately weigh an appropriate amount of the required base ink (such as 10g), pick up a small amount of each base ink with an inking knife and adjust it evenly on the glass plate, visually mix the ink color with the original color, and adjust it while measuring. When the adjusted ink color is close to the original color, you can take the adjusted ink on the scraping paper for scraping, and carefully compare the face color, base color, and ink color. After repeated and careful work of mixing, 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, and then weigh each base ink with this amount for deployment, scraping and color comparison, correct the ink color of the blended ink to be consistent with the original color, and finally enlarge the amount of ink required by this small sample proportion

3 inkability

3.1 allocation of printing adaptability

(1) viscosity and its allocation. Viscosity is the main performance index of gravure ink printing suitability. The viscosity of plastic gravure printing ink is lower than that of other inks, only 50 ~ 110cp/25 ℃ (coating Cup: 30 seconds/25 ℃). The viscosity of ink is too large or too small, which is not conducive to the printing operation. The viscosity is too high, the manufacturing technology and equipment are backward, the range production enterprises have not been formed, and the market competitiveness is insufficient. As a result, the ink transmission is not smooth in the transmission process, the transfer printing is poor, and the printing materials bite color, paste plate, peel and other faults occur; 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 the ink, if the viscosity is too large, 5% ~ 15% of the special mixed solvent for plastic gravure printing ink can be used for mixing. This mixed solvent is composed of ethanol: isopropanol: 200 # solvent: butanol =1.4:2:6:1:1. Do not add solvents indiscriminately during adjustment. If the viscosity is too small, you can use the same kind of new ink with higher viscosity for blending

(2) viscosity and its blending. Viscosity is a performance index that characterizes the ability of ink to resist ink film separation in the transfer process. Plastic gravure printing inks are thin and low viscosity, and viscosity is usually ignored. In fact, improper viscosity will also cause poor adaptability of printing operations, further affecting the printing quality. If the viscosity is too large, there may be faults such as the back color pulling out the front color, blocking the plate, uneven imprinting, and no light after drying when the front color is not completely dry. The solution is to use the adhesive remover appropriately

(3) liquidity and its allocation. Fluidity is related to viscosity, viscosity, thixotropy, silk head and consistency, and is affected by the characteristics of binder, the structure of pigments and fillers, and the content of solids in ink composition. If the fluidity of plastic concave ink is too large, there will be faults such as pattern expansion, unclear level, ink color unsaturated, and color and luster not bright. These faults can be adjusted by changing the formula during ink design, and new ink with small fluidity can be adjusted or replaced during production site use; If the fluidity is too small, there will be poor ink transmission, uneven inking, and inconsistent ink color. This phenomenon can be adjusted by mixing diluent (ethanol: isopropanol: 200 # solvent: butanol =1.4:2.6:1:1)

(4) foam and its elimination. Plastic concave ink is low viscosity, thin and liquid, and ink pump is often used to supply ink circularly in the printing process. Air will inevitably mix into the flowing ink, and bubbles will be formed due to the large surface tension of ink. Foaming affects the normal operation of printing. The way to eliminate foam is to add defoamers with an ink amount of 0.3% - 0.5%, such as organic silicone oil; 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 below 30cm into the liquid level of the ink bucket

(5) stability and its allocation. The stability of plastic concave ink refers to the continuous uniformity of the ink in the process of storage or use. Because plastic concave ink is a thin and low viscosity liquid, it often appears the phenomenon of pigment, filler and binder delamination, 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 adjusted by adjusting the formula design; It may also be that the excessive dilution in the use process has broken the liquid-solid balance of the ink, 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. Therefore, it is necessary to shake the ink sufficiently before using it

3.2 allocation of printing quality suitability

(1) dryness. Plastic concave drying should not be done on the machine, but quick drying after printing. Too fast drying will cause blocking, no imprinting or incomplete imprinting during the transmission of ink; Too slow drying will cause printing faults such as dry after printing, sticky imprinting, dot expansion, unclear layers, roll and roll bonding, etc. At present, when the ink is used, if it dries too fast, an appropriate amount of solvent with high boiling point can be added; if it dries too slowly, an appropriate amount of solvent with low boiling point can be added

(2) adhesion. The adhesion of plastic concave ink refers to the adsorption and adhesion of the dry printing film on the surface of the substrate. Plastic gravure printing ink because the substrate is a polyolefin material with smooth surface and weak polarity, the adhesion of the printing film on it is relatively difficult. The main way to solve the adhesion problem of the printing film is to polarize the plastic surface, but in terms of printing ink, one is to choose polyamide resin ink with greater polarity; The second is to choose resin diluent and diluent when diluting and diluting

(3) resistance. The resistance of plastic concave ink is mainly the durability and color retention of fingerprint film to ultraviolet light, water, organic solvents, acid and alkali solutions. Durability is affected by the performance and dosage of resin, pigments, fillers and additives. Durability can be improved to a certain extent by changing the formula structure

(author: Cui Jinfeng, Zhou Yingping)