Influence of thixotropy of the hottest ink on prin

2022-08-11
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Influence of ink thixotropy on printing quality

ink thixotropy is one of the properties of printing process, which has a great impact on the quality of printing products. Thixotropy refers to the phenomenon that ink thins or thickens and its fluidity changes under the action and influence of external forces and external environmental factors. For the printing process, the stable printing quality of products requires the ink to maintain a moderate and stable liquidity. However, due to the inherent factors of the ink itself and the printing conditions, the ink will inevitably appear "thixotropic" phenomenon in the printing process, which affects the stability of product quality. Therefore, we should correctly understand the thixotropy of ink, take some measures to overcome and make up for it from the process and technology, and reduce the thixotropy degree in ink printing, so as to better ensure the printing quality of products. Understanding of ink thixotropy

in the production process practice, we found that generally, ink has a certain thixotropy, which is mainly manifested in that the ink becomes thin after stirring and friction, so that the fluidity increases, and after it is left for a period of time, the ink will return to its original thicker state. For example, the ink with high viscosity has a certain fluidity when its solidification state is destroyed under the agitation of external forces. In the static state, with the increase of time, its solidification state gradually increases. When it is restarted, it will affect the normal flow of ink in the ink bucket, and even fail to transfer. On the other hand, the temperature of the ink on the ink bucket and rubber roller of the printing machine rises after rotating friction, so the fluidity and ductility also increase. Until it is transferred to the printing sheet, due to the disappearance of external force, its fluidity and ductility decrease, and then it changes from thin to thick, so as to ensure the clarity of the printing ink. In addition, when the temperature is low, the ink appears thick; On the contrary, the ink becomes thinner and the fluidity increases. When the machine is shut down for a long time, the ink in the ink bucket will gradually return to its original state from thin to thick. These are normal phenomena of ink thixotropy

generally, during the printing process, the vast majority of inks will become thinner from thickening, which is caused by temperature changes, such as machine temperature rise, ink roller temperature rise, printing plate temperature rise, etc. When the ink has certain thixotropy, it is conducive to the smooth and uniform transmission and printing of the ink

in addition to the above factors, the thixotropy of inks is mainly determined by the composition characteristics of inks. For example, inks made of pigments with strong surface adsorption have large thixotropy; The thixotropy of the pigment in the ink is larger than that of the spherical particles in the form of needle and plate particles; If the amount of pigment is large, its thixotropy is also large, because the pigment molecules attract each other and flocculate; If the wettability of pigment and binder is poor, the thixotropy of ink will be large; If the resin molecule ratio is large, the thixotropy of ink is also large. In addition, the thixotropy of pigment based inks is relatively large, which is due to excessive pigment content and poor pigment quality in inks, such as poor wettability and low relative density, resulting in low coloring power of inks. This problem also occurs when there is too little binder in the ink and the viscosity is too small

impact of ink thixotropy on printing quality

it can be said that the thixotropy discomfort of Wang cuifen, Secretary General of the waterproof materials professional committee of the China Construction Association of inks, has a great impact on printing quality. In production practice, we found that in the printing process, especially in the case of low temperature and slow machine speed, the ink in the ink bucket often has the phenomenon of unsmooth transmission and abnormal ink supply, which can create a lot of economic benefits for enterprises As a result, the ink color of printed matter becomes lighter and lighter, which affects the stability of printing ink color, which is the main manifestation of poor thixotropy of ink. In this regard, we should always pay attention to mixing the ink in the ink bucket to maintain continuous and uniform fluidity and ensure the ink quality of the product

some inks have high viscosity before thixotropy due to their high thixotropy during transmission, which is easy to cause ink blocking and plate pasting during printing. Therefore, some printing machines are equipped with agitators in the ink bucket to stir the ink to make it "thixotropic" to improve the flow of ink and reduce the viscosity of ink, so as to prevent the phenomenon of ink blocking and pasting. If the thixotropy of the ink is too large, the ink in the printing process becomes thinner and thinner, and the ink color of the printed matter becomes thinner and thinner, which is almost impossible to adjust, this kind of ink is not suitable for printing full-size printed matter on the spot. This problem should be paid attention to when printing

technological measures to control ink thixotropy

printing requires ink to have appropriate thixotropy. Too large or too small ink thixotropy will have a negative impact on printing. The thixotropy of ink is mainly determined by its material characteristics, but as mentioned above, printing conditions will also affect the thixotropy of ink to a certain extent. Therefore, when the inherent thixotropy of ink cannot realize normal printing, corresponding control can be carried out through technological measures. For example, the appropriate ink fluidity can be adjusted according to the characteristics of the printing machine and the temperature. When the printing speed is low and the temperature is low, because the thixotropy of the ink is small, its fluidity is also small, which is not conducive to uniform ink transmission and inking. At this time, the ink can be thinned appropriately to meet the requirements of the printing process

in order to prevent the adverse effects of excessive "thixotropy" of ink on printing, it is necessary to control the printing process conditions to control the thixotropy of ink within the range of printing suitability. First, try to print in a constant temperature and humidity environment and install air conditioning equipment in the production workshop. If the conditions are limited, when the weather is dry and windy, the doors and windows of the workshop can be closed to prevent the ink from thickening and sticking; Second, when the thixotropy of the ink itself is too large, the printing speed should be controlled within the minimum range as far as possible, so as to reduce the temperature rise of the ink due to the high friction coefficient of the machine, so as to make the ink thinner; Third, under the condition of not affecting the uniformity of the layout and full inking, the number of inking rollers on the machine should be reduced as far as possible to reduce the friction coefficient during printing; Fourth, adjust the position of the ink roller and water roller on the machine to prevent the ink from thinning due to the excessive contact between the ink roller and the ink roller, between the ink roller and the plate, or between the water roller and the plate, and the abnormal temperature rise caused by the large friction coefficient; Fifth, control the rotation stroke of the ink bucket roller. If the rotation stroke of the ink bucket roller is large, the temperature rise will be high, and the ink will easily become thin. Therefore, in the case of high printing speed, the rotation stroke of the ink bucket roller should be reduced as much as possible, and the gap between the ink bucket steel sheet and the ink bucket roller should be appropriately increased to meet the printing ink supply requirements; Sixth, when the relief (including flexo) printing layout is large, the printing speed should be controlled lower to reduce friction and temperature rise; Seventh, the printing ink should be selected reasonably. The thixotropy of the printing ink is required to be slightly larger for the printing line version, and slightly smaller for the printing of large-area field version, so as to better improve the printing quality

to sum up, ink thixotropy has a certain impact on printing, and the factors affecting ink thixotropy are various. Therefore, it is of great significance to correctly understand the thixotropy of ink and its related factors, take corresponding technological measures for appropriate control during printing, and keep the ink in a relatively stable state in the printing process, so as to effectively avoid the production of printing quality defects in one way or another, and improve printing efficiency and product printing quality

source: (excerpted from China Packaging News, author Kang qilai)

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