Application of the hottest filter paper in printin

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Application of filter paper in printing machine inking

the ink in the printing machine inking system, after being transferred to the substrate, solidifies rapidly to form an ink film resistant to mechanical friction. This change from fluid to solid is called ink drying. The time required to complete this change process is called drying time. The drying time is short, and the ink drying speed is fast; Long drying time and slow drying speed of ink

ink drying is generally carried out in two stages. The first stage is that the binder in the ink penetrates into the paper layer (or the solvent in the ink volatilizes), the adhesion of the ink film increases, and the stage of losing fluidity is called the fixation of the ink. The second stage is the stage when the ink changes physically and chemically and is firmly bonded to the surface of the substrate, which is called the curing of the ink. It is difficult to strictly distinguish the fixation and solidification of ink in the whole process of ink drying

the drying speed of imprinting has a great impact on the printing quality of printed matter. If the drying is too slow, the back of the printed matter will be rubbed and dirty, or the printed sheet will stick to the page; Drying too fast, the ink crusts in the layout and blocks the pattern, which not only reduces the clarity of the image, but also causes the ink to accumulate, and the printed products appear "ink spots". Therefore, by analyzing and researching the transfer investment focus of China's chemical industry, aiming at new materials, studying the law of imprint drying, controlling the speed of imprint drying in production, and making the imprint dry in time, we can obtain high-quality prints with full ink, bright colors, rich layers and high gloss

the drying process of ink is an extremely complex physical and chemical process. The speed of ink drying is related to the form of ink drying, the performance of printing materials, printing process conditions, environmental temperature and humidity and other factors

I. factors affecting the drying speed of imprinting

the drying speed of ink refers to the time required for the ink on the print to completely solidify. The shorter the time, the faster the drying speed of imprinting

1. Ink drying form. In 3D printing, degradable plastics become a new favorite. Different substrate surfaces are printed by different printing methods, and the drying form of ink is also different. For ordinary printing such as lithography, letterpress, gravure and perforated plate, the ink on the printed matter generally depends on infiltration, oxidative polymerization, volatilization, UV (ultraviolet) and other forms of drying

① osmotic drying. After the ink is transferred to the porous substrate surface, under the action of capillary, part of the ink is connected and penetrated into the interior of the paper, and the other part of the binder is fixed on the substrate surface together with the pigment. The drying of the ink mainly depends on the capillary absorption of the substrate. This kind of ink drying is called osmotic drying. The process of infiltration drying is that the substrate absorbs the binder in the ink. Because there are also tiny gaps between the ink and pigment particles, the capillary effect formed by these gaps is to prevent the ink from penetrating. When the capillary action of the substrate is balanced with the capillary action between the ink pigment particles, the binder in the ink stops penetrating into the substrate, and the ink on the print dries

in the actual printing process, the penetration of ink into the substrate goes through two different stages. In the short time when the ink on the printing plate contacts with the paper, the ink penetrates into the surface of the substrate under the action of printing pressure, which is pressure penetration; When the substrate leaves the embossing area, the ink transferred to the substrate penetrates into the inner layer of the substrate by the force of capillary, which is the time of free penetration, pressurized penetration and free penetration, which can be expressed by the following formula:

pressurized penetration time:

tpressure =4 η H2 pressurization/p-2r ()

free permeation time:

tfree =4 η H2free/r γ ()

see equations () and () for the derivation of the above two equations. Where η Is the viscosity of the ink, h is the penetration depth of the ink into the substrate under pressure, h is the free penetration depth, and R is the average capillary radius of the porous substrate, γ Is the surface tension of the ink. () and () show that the ink drying speed is fast when printing with low viscosity ink on a substrate with loose texture and strong porous absorption. High speed relief rotary ink, the binder is composed of mineral oil and asphalt resin. This ink is used to print on paper with good absorption. The drying of the imprint is completely completed by infiltration drying. However, if the printing pressure is too high and the viscosity of the binder is too small, the "through printing" fault often occurs

② oxidative polymerization drying. The ink with dry vegetable oil as binder will undergo oxidative polymerization reaction with oxygen in the air, so that the dry vegetable oil molecules distributed in three-dimensional space become giant molecules with three-dimensional structure, which will be dried and fixed on the surface of the substrate. This kind of oxidation polymerization reaction is called oxidation polymerization drying, which makes the ink change from liquid state to solid state and forms a solid impression on the surface of the substrate

the reaction of dry vegetable oil in ink from liquid to solid is very complex. Generally, it needs to be polymerized through peroxide bridge or conjugated double bond addition polymerization, and the reaction takes place on the double bond of unsaturated acid. With the progress of the reaction, the molecular chain gradually increases, and the viscosity of the ink gradually increases until all the double bonds of unsaturated acid are reacted, and the ink is completely dry. Therefore, the more double bonds of dry vegetable ink, the faster the oxidative polymerization drying speed

the oxidative polymerization reaction speed of dry vegetable oil is relatively slow, because dry vegetable oil contains a small amount of phosphorus ester organic antioxidants, coupled with other effects of blocking drying, it absorbs less oxygen, which is the induction period of the drying process, during which dry vegetable oil basically does not change. Therefore, the drying time of oxidative polymerization of dry vegetable oil generally takes several hours, or even as long as several days. In order to speed up the reaction speed of oxidative polymerization, antioxidants must be destroyed to make dry vegetable oil absorb oxygen in the air and form peroxides, which are used as the media to initiate the polymerization of double bonds

adding a drying agent (i.e. drying oil) to the ink with dry vegetable oil as the binder can accelerate the drying of the ink. The addition of driers, on the one hand, can oxidize the antioxidant in the ink or combine it with antioxidant substances to form precipitation, so as to remove the interference of antioxidant on oxidative polymerization reaction and shorten the induction period; On the other hand, driers can also promote polymerization

lithography is mostly printed on coated paper with relatively tight texture and low absorption, and the ink on the printed matter mainly depends on oxidation polymerization and drying

③ dry volatilization. The ink transferred to the surface of the substrate, the organic solvent molecules with large energy in the binder, overcome the mutual attraction between the molecules in the ink and escape to the air, and the remaining resins, pigments and other components thicken and solidify rapidly. This form of ink drying depends on solvent volatilization, which is called volatilization drying

volatile dry inks and binders contain volatile solvents, such as water, benzene, xylene, esters, alcohols with low carbon chains, etc. The speed of evaporation and drying mainly depends on the evaporation speed of the solvent and the evaporation latent heat of the solvent

table boiling point, latent heat of evaporation, volatilization rate of common solvents in ink

solvent name boiling point range (℃) latent heat of evaporation (kcal25/kg) volatilization rate (s)

ethyl acetate 72 ~ 8040185

toluene 109 ~ 112400 180

ethanol 75 ~ 80810240

water 100 2291 1120

the volatilization rate of solvent can be expressed by the number of seconds (s) it takes 1ml of solvent to completely volatilize on the filter paper. Latent heat of evaporation refers to the heat energy required when a certain amount of solvent turns into gas. The lower the boiling point of the same kind of solvent, the higher the volatilization rate; However, different types of solvents have low boiling points, but the volatilization rate is not necessarily fast. The table lists the boiling point, latent heat of evaporation and evaporation rate of solvents commonly used in several inks. The boiling points of ethanol and ethyl acetate in the table are similar, but the evaporation rate of ethyl acetate is more than twice that of ethanol, because the latent heat of evaporation of ethanol is higher than that of ethyl acetate. The smaller the evaporation latent heat of the solvent, the higher the evaporation and drying speed

volatile dry ink is mainly composed of solvent, resin and pigment. Because resin molecules and pigment molecules exist on the surface of the ink, there is a strong traction between solvent molecules, resin molecules and pigment molecules, which makes it difficult for solvent molecules to escape into the air, so the volatilization speed of the ink is lower than that of the solvent

different resins have different degrees of slowing down the speed of solvent volatilization. The greater the solubility of the resin, the more difficult it is for the solvent to be separated from it. When using solvents with different boiling points and adjusting the evaporation and drying speed of the ink, the resin in the ink must have a certain release to the selected solvent. Otherwise, in the printing process, the dissolving and forming of a mature composite stator blade process and technical system, it is difficult to release the agent, the ink on the printed matter is not dry, and it is easy to have the fault of "back rubbing dirty"

in addition, the volatilization rate of solvent is also related to the external temperature and vapor pressure. The higher the external vapor pressure, the higher the temperature. In the final analysis, the reason for this kind of scene is that the friction coefficient function of plastic flexible packaging materials develops faster

when printing on the surface of non absorbent substrate, the ink on the printed matter mainly depends on the evaporation of solvent to complete the drying

with the development of high-speed, multi-color and multi variety printing, mixed dry ink is mostly used in printing. For example, letterpress resin printing ink mainly depends on penetration drying, but it also includes oxidative polymerization drying; Fast fixing resin ink, using penetration drying to accelerate the fixation of ink, using oxidative polymerization drying to complete the curing of ink; Thermosetting inks use volatile drying to accelerate the initial drying of inks. The drying form of mixed ink makes the drying of imprinting more complicated

source: Nantong Sanmu precision filter paper Co., Ltd

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