The pigments (colorants), fillers, binders, and adjuvants are mixed and ground to uniformly distribute the pigments, fillers, and adjuvants in the binder, forming a colloidal dispersion system with a uniform and delicate appearance. Or paste, this is the ink.
Due to the different printing processes, inks are required to have different properties. If the gravure ink is thin, the adhesiveness is also very small, otherwise it can not be filled into the plate. Can not be scraped clean by the scraper. The ink is mostly used for letterpress printing presses. The printing speed is up to 10,000 printing/hours. The paper used is good newsprint. Therefore, the ink is only slightly thicker than gravure ink. , And the penetration and drying are very good. Otherwise, it will not meet the requirements of high-speed printing and rapid drying. The letterpress rotary printing machine of the book is slower, and the used paper is more solid and less absorbent. Therefore, the ink in the printed book is thicker and stickier than the ink, and the permeation and drying properties are slightly slower. Some of them even have the property of a part of the oxidized aggregate film drying. The writing of the books and magazines can be printed more clearly and it is not easy to erase them after drying. Color letterpress printing is mostly used for printing logos, packaging, and other prints, and the printing speed is slower. The paper used is from relief paper, offset paper, coated paper, and glass powder-coated paper. The printed matter is required to have vivid colors and clear graphics, solid general letterpress inks, or color lead inks, and other inks (including copper and zinc inks). The inks are much thicker and more sticky than the inks. Otherwise, dot prints are not clear. Because the printing speed is slower and the paper absorbs poorly, the solid-oxidation-polymerized conjunctiva is dried. In addition, it must be colorful and have a certain degree of luster. As for printed copper plated paper, coated paper and other printed materials, offset printing inks with higher color density are generally used, and even bright light fixes the offset printing inks in order to obtain bright colors and excellent gloss. Offset printing uses the oil-water mutual exclusion principle to print, so the offset ink must have a certain water resistance and should not be heavily emulsified on the printer and bleed in the solution. Because the offset printing speed is now faster than embossing, and after rubber transfer, the viscosity of the ink must not be too high, so its thickness is less than that of colored lead ink and its viscosity is also small. All the papers used are offset papers and coated papers, so they are also dry for oxidative polymerization. Some require that the back surface is not stained, so it is necessary to fasten the ink. If you want good gloss, you need to fix the ink with bright light.
The nature of the ink is actually determined by its composition, such as the color, tinting strength, light resistance, acid resistance, alkali resistance, soap resistance, heat resistance, resistance to various solvents and water resistance of the ink, and is mainly determined by the pigment. The properties of the ink such as drying property, fast fixing property, glossiness, friction resistance, flex resistance, etc. mainly depend on the binder. The viscosity, viscosity, fluidity and other properties of the ink are largely related to the binder but are also related to the nature and amount of the pigment and filler used. Therefore, the ink worker should understand the characteristics of the printing process and the substrate before designing to design and manufacture the ink that meets the requirements. The printers should also have a certain degree of understanding of the nature of the ink in order to use the ink properly.
1. Color tinting strength and transparency
The color of the ink, especially the color of the ink of the three primary colors, is often measured in terms of density, color difference, grayscale, and actual color efficiency in printing, and is generally measured and calculated by a color density meter in a solid or color part of a printed matter or proof. Got it. However, to measure the quality of ink, a certain amount of ink must be taken in accordance with the international standard method. The IGT fitness tester prints the color block on the specified coated paper with a certain pressure and printing area, and then uses a color densitometer. Make measurements and calculations. Otherwise, these valid data are not standard and comparative.
For trichromatic inks, the color density should be within a certain range, usually 1.00 ± 0.05 for yellow, 1.45 ± 0.05 for magenta, and 1.55 ± 0.5 for cyan. However, due to the different requirements of the original color tone, it may be slightly different. When the density of the three primary colors is within the above range, the gray balance can generally be achieved, and the color difference, grayscale, and actual color efficiency thus calculated are also of practical significance. The standard color ink that meets the ideals of the three primary colors in the world does not exist. However, the smaller the color difference should be, the better the gray balance and the reproduction of the original color are. When the grayscale is small, that is, the brightness is high, when the color of the original is very vivid, the three primary colors having a large grayscale cannot reproduce the bright original color. As for the drawing or some of the original tones that are relatively dark, the gray scale of the three primary colors is not necessarily required at the time of printing, and sometimes the grayscale or the underprint or spot color is increased. The actual color efficiency refers to the purity of the main color tone, and the higher the color efficiency, the larger the range of the solid color matching with the other two three-primary inks. In general, inks with small color casts and small gray scales have greater actual color efficiencies. To measure the color quality of the three primary color inks, it should generally be small in color, small in gray scale, and the actual color efficiency is better.
The coloring power of ink is also known as the color density, the ink with large coloring power, the smaller ink amount can make the printing part reach a certain color density, and the ink with small coloring power needs to use a larger amount of ink. Disadvantages in the printing process, such as network expansion, stencil or even dirty. However, it should be noted that inks with large coloring power also have large gray scales and affect the vividness of color. Therefore, the coloring power of the three primary color inks should be equivalent to the three. When the coloring power of one of the colors is too large or too small, it will affect the gray balance and color reproduction.
The transparency of the ink is also very important, the transparency of the three primary inks must be more than 90% in order to better represent the intermediate color and discoloration. For example, in the past, the transparency of yellow was not good, at around 85%. At that time, the general printing sequence was yellow, yellow, blue and black. Yellow ink is the bottom, opacity is also not good, so no problem occurs. Recently, black, blue, yellow, and yellow ink are the last to print. When the transparency is not enough, the yellow version is heavy, and the ink layer is thicker, so that the entire screen is covered with a faint color.
In the packaging printing, often use the background color to highlight and highlight the theme, usually pink, orange, orange, orange, yellow, light blue, lake blue, grass green, light green, brown, brown, beige, snow, Light gray and other colors, which have an understanding of the color properties of the ink can be handy to obtain the desired color. The following points should be noted.
1 The color matching of ink is a subtractive effect, and the more the colors are, the darker and darker it is. Therefore, the color should be used as little as possible. First, it should be adjusted with two colors. After adjusting to a very close value, add a third color. Micro adjustments to achieve the desired color. Because the background color is often pale, the final rinse ink is added to lighten it. A small amount of flushing can be done first, and it is considered that the requirement is enlarged again, so as not to waste too much at once, especially after diluting, there is still a certain gap. Additions and adjustments, the more you work together, the more you work together, the more you fight, the more you exceed the amount you need. The color ink supplied by the ink factory has many intermediate colors and color changes in addition to the three primary color inks. When the ink is adjusted, two kinds of close color tones may be taken as necessary to achieve the requirement that the color tone is relatively clear and not too dark. Below there is a color ring diagram, arranged the name of the various inks, two kinds of colors close to the color of the mix more distinct, far away from the distance becomes gray. If you want to mix fresh grass green, you can use lemon yellow (yellowish) and green, when using yellow and medium blue, the emerald green is very dark.
2 When the color is washed with light, the color of the clear ink is dark, but it is not dark on the white paper. Diluting with white ink, the ink looks brighter but pink. Requests light color without pink and bright, and some people often add a small amount of white ink when using a large number of transparent dilute inks, although in the hue to achieve brighter requirements, but the white ink makes the ink with poor lightfastness easier to fade Disadvantages must be noted. Therefore, it is best not to add white ink when paper with good whiteness is light, and paper with poor whiteness is different.
3 The flesh color is also often diluted with gold and red ink, although the hue is good, but after the red light fades easily, it is not appropriate. Pink ink is also easy to fade after dilute. Diminishing the tone with darker 05-06 or darker 05-06, the fade is much better. When the yellow tone is not enough, the orange ink is slightly added. This ink is also good in light resistance and is not easy to fade. Light blue lake blue should be diluted with sky blue ink, do not use medium blue or dark blue, because it is easy to fade. Green ink and Qinglian ink have good lightfastness and lightfastness. They should also use lightfastness when lightening, otherwise they are easy to fade. The yellow ink is now lightfast than the sky blue ink and green ink, so when adjusting the green color should be considered in the future yellow will first fade, you need to pay attention to display the window packaging print.
4 Packaging printing sometimes uses aluminum foil or thin sheet metal. This often needs to consider the transparency of the ink in the background or pattern printing. The effect of the opaque yellow ink and the transparent yellow ink on the aluminum foil or iron sheet is completely different. A lot of candy-wrapped aluminum foil or tin box, first printed with a layer of transparent yellow ink, can make the metallic luster reflected through the yellow ink layer to become a golden color. The yellow ink with low transparency is very ineffective, and the use of high-transparency Taohong or magenta ink, sky blue ink, and green ink ink background color can make the aluminum foil or tin box show a very beautiful, vivid and bright color. Sometimes white ink is used to make the bottom, which is a complete requirement to cover the metallic luster of aluminum foil or iron sheet, and then print it like a pattern printed on white paper.
2. Fineness
The fineness of the ink is measured by a scraper fineness meter, which indicates how large the diameter of the largest solid particle in the ink is. Generally, the fineness of the letterpress ink is less than 20 microns, and the offset ink is less than 15 microns. This data is actually the diameter of a solid surface wrapped with a thick layer of oil. The diameter of a true solid is only half the size, ie, the relief base is less than 10 microns, and the offset ink is 7.5 microns or less. The so-called maximum particles account for a very small number of particles in the total solid particles of the ink, and most of the ink particles are much smaller. Even with the 15 micron count, the area of ​​the printed dot network is compared to the area of ​​the ink particles, or a dot can accommodate many ink particles. See Table 1 for details. The area of ​​the 250 lines listed in the table is also more than that of the 15 micron ink particles. The area is 6 times larger, and 40% is 23 times larger. Moreover, the vast majority of ink particles are much smaller than 15 microns. Therefore, the qualified factory ink will generally not affect the printing quality due to fineness problems.
A site survey was conducted on the problem of printing quality that affects the quality of printed matter due to poor printing ink quality. Except for a small amount of ink, the ink was thickened due to long-term storage of particles, or improper storage and use, and the surface of the ink was clogged. Most of the paper is deinked and mixed into the ink to cause ink thickening.
3. The rheology of ink
Offset or embossed inks are all sticky, thick paste-like bodies, which are physically called plastic fluids. They do not deform or flow like an ideal fluid (water) with external force. They must be added to a certain degree to start deformation. Or flow. As shown in Fig. 2, when the external force is applied, the ink does not flow, and the rheology that begins when the force reaches point A is added. The flow deformation at this time is a trend that is almost a solid movement and is called a plug flow. That is, the curve AC' in the figure indicates the relationship between force and rheology. When the force increases to C', the rheology of the ink flows like a perfect fluid in a laminar flow, and the rheological curve is linear. The force A that causes the ink to begin its rheology is called the minimum yield value, and the force C that causes the ink to start laminar flow is called the maximum yield value. The extension of the line above the C' point and the axis of force are changed to point B. The force at point B is called the ideal yield value. A preliminary understanding of the rheological properties of the ink's plastic fluid can be studied against the printing process's requirements for the ink's printability.
1viscosity, yield value and thixotropy and their determination
Relief and offset inks are viscous, thick plastic fluids. To determine the internal resistance of a flow, the so-called viscosity, first of all overcome the internal stress corresponding to the minimum yield value, so the Ford cup (paint cup) or falling ball The viscometer is not suitable. A peristaltic viscometer, drop bar viscometer, or parallel plate viscometer is typically used to determine the viscosity and yield value, or to characterize rheological curves to investigate its rheological and thixotropy properties.
â— Rotary viscometer
Commonly used are the Bruker Vist Viscometer and the Hermite Viscometer, the latter being used domestically. Its structure and principle is that the ink is placed in a small cylinder that can be kept warm. A rotor is inserted in the ink. When the rotor is rotated, the spring connecting the rotor is deflected by the viscosity of the ink, and the pointer is moved to directly read the viscosity. . By changing the cylinder and rotor and changing the rotation speed by the gearbox, the viscosity of various inks can be measured from 0 to 1.000.000 centipoise. The structural principle of the Bruker Vist Viscometer is basically the same as that of the Hermite Viscometer. However, it is possible to change a lot of speeds step by step, from the lowest speed step by step to the selected highest speed to determine a series of letterpress and offset inks. The data pairs for shear rate and shear stress will be depicted as an upwardly curved curve. A series of shear rate and shear stress data pairs are then determined as a straight line by stepping from the highest speed to the lowest speed. As shown in Figure 3. The size of the area surrounded by the two lines indicates the size of the touch. Actually, this is because the pigment particles in the ink attract and flocculate each other when they are at rest, so that they are in a thick condensed state. When the mechanical stirring force is applied, the flocculation force is destroyed and the thin and easily flowing state is achieved. But after a period of rest, it will flocculate again. This is the touch.
â— Drop stick viscometer (Raleigh viscometer)
The main structure is a horizontal short cylinder mounted on a vertical support, which is hollow and straight. A long round rod is inserted into the empty cylinder. The round rod and the cylinder have a certain gap. The ink is added in a certain amount in the gap, so that the round rod and the round The middle of the barrel is filled with ink, and weights of different weights are placed on the round bars. Determine the time required for the free fall of the round bar by 10 cm. Due to the resistance of the viscosity of the thin layer ink when the round bar falls, and because of the different weights on the round bar, different times are required to express the shear rate of the ink, and the ink flow curve can be plotted and calculated accordingly. Theoretical yield value and plastic viscosity.
â—Parallel plate viscometer
A certain amount of ink is placed between the two flat plates placed horizontally. The upper plate has a prescribed weight and can be freely dropped horizontally at a fixed height and pressed against the ink. The ink is circularly arranged in two parallel directions. The middle of the board is expanded. The diameter of the ink spread increases with time, and the diameter of the ink spread is recorded at different times of 10 seconds, 60 seconds, 100 seconds, etc., and the slope, intercept, and yield value of the ink rheological curve can be calculated.
2 stickiness and its determination
When the ink is run on the ink roller of the printing machine, it is torn by the ink roller that rotates in the opposite direction. The resistance generated at this time is called the viscosity of the ink. This is the comprehensive force that the ink's cohesion and adhesion are balanced with each other. Performance. Unlike the viscosity of the above ink, there is no absolute unit. The viscous index is measured with an ink gauge (ink stickiness meter). Its main structure is the three ink rollers and the connected weights and balances. When a certain amount of ink runs between three ink rollers at a certain temperature, the ink layer is The resistance of tearing is transmitted to the balance bar, and a viscous reading is obtained with the weight hit. The use of tack to study the transfer of inks on printing presses is more practical than viscosity, and has therefore been valued by the ink and printing industry in the world.
3 fluidity and its determination
0.1 ml of the ink was subjected to a total weight of 250 g in a round glass sheet having a diameter of approximately 70 mm at a temperature of 25°C. After 15 minutes, the ink was flattened to expand into a circular diameter of mm. This is a comprehensive representation of the thickness, soft and hard viscosity, and yield value of the ink.
4The relationship between various rheological properties and printing adaptability of ink
Because letterpress and flexographic printing inks are plastic fluids with more complex rheological properties, the structure and properties of various printing presses have different requirements for inks. Therefore, the relationship between the rheology of these various inks and printing suitability It is also related to each other and is very complicated. We can only give a rough introduction here.
Viscosity for letterpress and offset inks is not as obvious and strictly related to printing as for flexographic inks and gravure inks, but there is a general rule that the printing speed is slow, and higher viscosity inks can be used; the printing speed is high. The ink used has a lower viscosity. Such as the wheel transfer ink is much smaller than the ink viscosity. Offset inks used in high-speed four-color offset presses are less viscous than offset inks used in general-purpose monochrome or two-color offset presses. However, the viscosity of the ink becomes smaller as the temperature increases. After the high-speed offset printing machine is opened, the ink roller has a high speed and a high temperature rise, the viscosity of the ink will gradually become smaller, so the viscosity is slightly higher, and the substrate has a relationship with the viscosity of the ink. The smooth and solid paper can be used at a high level. Viscosity of the ink, the structure of loose paper on the use of smaller viscosity ink, otherwise it is easy to fall powder, hair removal.
Viscosity and viscosity are related, that is, the viscosity of the ink with large viscosity is generally high. However, there are also irrelevant times, so some inks have similar viscosity but different viscosities. Some inks have similar viscosities and different viscosities. In this case, the ink should be selected mainly for stickiness. For example, the color offset ink has a viscosity in the range of 5-9. The applicable range of the color printing ink viscosity is 5-11. The offset printing ink has a much faster printing speed and the applicable adhesive range is 3-6. The viscosity of the ink has a great relationship with the printing speed, the separation speed of the ink layer at the printing speed is also fast, and the viscosity exhibited by the ink is also large, which is the main reason why the offset of the offset printing ink is particularly low. Viscosity has a great influence on ink transfer and ink distribution. In the applicable range, inks with higher viscosity are better for ink transfer. The ink layer printed on paper is also thicker and the dots are more realistic. However, when the viscosity is too large, unevenness occurs on the ink roller or even the roller stacker or the stacker rubber. At this time, the dots of the print are also hairy and false. When the viscosity is too small, the ink transfer is poor, and the ink layer printed on the paper is thin at the end, and it is easy to expand the dots. The viscosity of the ink is very much related to the paper. For example, the same sticky ink is printed on the offset printing machine. The relatively solid imported coated paper can be printed well. Switching to the poorer coated paper produced by China will cause the powder to fall off and even peel off. It is the paper that cannot withstand the stickiness of the ink layer as it separates between the eraser and the paper. Viscosity is related to temperature. When the temperature is high, the viscosity is lowered. The offset printing machine pauses during the printing and then meets to cause the paper to lose skin. The reason is that the car has cooled for a while and the viscosity of the ink has increased. First print some good paper waste paper, the car will be normal after a period of time. In a four- or more-color offset press, the mutual stickiness of the four colors is also important. In general, the viscosity of the latter color ink cannot be greater than the previous color, otherwise it will pull down the previous color ink on the print.
The yield value and fluidity are related to the "body bone" of the ink. The so-called "body bone" ink is often a large yield value, and the ink surface with a large yield value looks harder on the ink body, and the ink is run on the ink roller. Shorter, less fluidity measured. In the proper range, the ink with the smaller yield value and greater fluidity is more suitable for printing on the embossing or offset printing machine. Due to the short drawing speed, less ink flying phenomenon, the harder fluidity of the ink body, and the smaller dot on the printing product thick. When it is too large and out of range, poor ink transfer is caused, unevenness is caused on the ink roller, and sometimes the ink is not discharged in the ink fountain.
The thixotropy of the ink is too large, due to the flocculating nature of the pigment particles, it can stop the ink from flowing for a short period of time due to flocculation. This is often due to the fact that the embossing and offset ink fountains do not release ink, resulting in the prints becoming more and more faded. The main reason. However, in the thixotropic inks, the printed dots are thicker, so it is not as small as possible. As to whether the scope of large or small is more appropriate, the general ink industry has not published any data.
4. Fixation and drying of ink
After the resin ink is printed on the paper, the low-viscosity solvent and dry vegetable oil can quickly penetrate into the pores of the surface of the paper, so that the synthetic resin and the dry vegetable oil remain on the surface of the paper and solidify. This state is called dryness. solid. At this time, a small amount of printing pressure on the back side will not stick on the back side, but the pressure will be too sticky. The solid ink layer is further oxidatively polymerized to form a firm film, which is truly dry. Generally, the resin ink has two stages of fixing and completely drying. The fast fixing ink is called fast fixing. The fixation is actually measured in seconds, but it is based on the test method and the instrument. The dryness is comparable to the time when the print is completely dry, in hours.
Fast fixing of the ink on coated paper or coated paper is remarkable because the pores on the surface of the coating are very fine and numerous. You can inhale an appropriate amount of solvent in a very short time and it is in a fixed state. The voids on the surface of a general offset paper are coarse and small, and a certain amount of solvent cannot be taken in a short time to fix the ink, so the effect is not good. The fixing state of the ink is not really dry, so only a small number of printing parts can be stacked and can not be moved by hand because the stacking excessive pressure is too large, or the local compression is too large by the hand-moving, only the fixing state The ink layer will still be damaged and make the back stick. The ink printed on the paper, whether fixed or not, due to the oxygen in the air, the unsaturated double bond of the dry vegetable oil acts, first the oxygen, then the polymerization, gradually increase the molecular weight and finally become a firm film, this is the real dry. Therefore, the conditions for the ink drying are the oxygen in the air and the heat or chemical accelerator that causes or promotes the oxidative polymerization, that is, the drying oil.
Due to the different printing processes, inks are required to have different properties. If the gravure ink is thin, the adhesiveness is also very small, otherwise it can not be filled into the plate. Can not be scraped clean by the scraper. The ink is mostly used for letterpress printing presses. The printing speed is up to 10,000 printing/hours. The paper used is good newsprint. Therefore, the ink is only slightly thicker than gravure ink. , And the penetration and drying are very good. Otherwise, it will not meet the requirements of high-speed printing and rapid drying. The letterpress rotary printing machine of the book is slower, and the used paper is more solid and less absorbent. Therefore, the ink in the printed book is thicker and stickier than the ink, and the permeation and drying properties are slightly slower. Some of them even have the property of a part of the oxidized aggregate film drying. The writing of the books and magazines can be printed more clearly and it is not easy to erase them after drying. Color letterpress printing is mostly used for printing logos, packaging, and other prints, and the printing speed is slower. The paper used is from relief paper, offset paper, coated paper, and glass powder-coated paper. The printed matter is required to have vivid colors and clear graphics, solid general letterpress inks, or color lead inks, and other inks (including copper and zinc inks). The inks are much thicker and more sticky than the inks. Otherwise, dot prints are not clear. Because the printing speed is slower and the paper absorbs poorly, the solid-oxidation-polymerized conjunctiva is dried. In addition, it must be colorful and have a certain degree of luster. As for printed copper plated paper, coated paper and other printed materials, offset printing inks with higher color density are generally used, and even bright light fixes the offset printing inks in order to obtain bright colors and excellent gloss. Offset printing uses the oil-water mutual exclusion principle to print, so the offset ink must have a certain water resistance and should not be heavily emulsified on the printer and bleed in the solution. Because the offset printing speed is now faster than embossing, and after rubber transfer, the viscosity of the ink must not be too high, so its thickness is less than that of colored lead ink and its viscosity is also small. All the papers used are offset papers and coated papers, so they are also dry for oxidative polymerization. Some require that the back surface is not stained, so it is necessary to fasten the ink. If you want good gloss, you need to fix the ink with bright light.
The nature of the ink is actually determined by its composition, such as the color, tinting strength, light resistance, acid resistance, alkali resistance, soap resistance, heat resistance, resistance to various solvents and water resistance of the ink, and is mainly determined by the pigment. The properties of the ink such as drying property, fast fixing property, glossiness, friction resistance, flex resistance, etc. mainly depend on the binder. The viscosity, viscosity, fluidity and other properties of the ink are largely related to the binder but are also related to the nature and amount of the pigment and filler used. Therefore, the ink worker should understand the characteristics of the printing process and the substrate before designing to design and manufacture the ink that meets the requirements. The printers should also have a certain degree of understanding of the nature of the ink in order to use the ink properly.
1. Color tinting strength and transparency
The color of the ink, especially the color of the ink of the three primary colors, is often measured in terms of density, color difference, grayscale, and actual color efficiency in printing, and is generally measured and calculated by a color density meter in a solid or color part of a printed matter or proof. Got it. However, to measure the quality of ink, a certain amount of ink must be taken in accordance with the international standard method. The IGT fitness tester prints the color block on the specified coated paper with a certain pressure and printing area, and then uses a color densitometer. Make measurements and calculations. Otherwise, these valid data are not standard and comparative.
For trichromatic inks, the color density should be within a certain range, usually 1.00 ± 0.05 for yellow, 1.45 ± 0.05 for magenta, and 1.55 ± 0.5 for cyan. However, due to the different requirements of the original color tone, it may be slightly different. When the density of the three primary colors is within the above range, the gray balance can generally be achieved, and the color difference, grayscale, and actual color efficiency thus calculated are also of practical significance. The standard color ink that meets the ideals of the three primary colors in the world does not exist. However, the smaller the color difference should be, the better the gray balance and the reproduction of the original color are. When the grayscale is small, that is, the brightness is high, when the color of the original is very vivid, the three primary colors having a large grayscale cannot reproduce the bright original color. As for the drawing or some of the original tones that are relatively dark, the gray scale of the three primary colors is not necessarily required at the time of printing, and sometimes the grayscale or the underprint or spot color is increased. The actual color efficiency refers to the purity of the main color tone, and the higher the color efficiency, the larger the range of the solid color matching with the other two three-primary inks. In general, inks with small color casts and small gray scales have greater actual color efficiencies. To measure the color quality of the three primary color inks, it should generally be small in color, small in gray scale, and the actual color efficiency is better.
The coloring power of ink is also known as the color density, the ink with large coloring power, the smaller ink amount can make the printing part reach a certain color density, and the ink with small coloring power needs to use a larger amount of ink. Disadvantages in the printing process, such as network expansion, stencil or even dirty. However, it should be noted that inks with large coloring power also have large gray scales and affect the vividness of color. Therefore, the coloring power of the three primary color inks should be equivalent to the three. When the coloring power of one of the colors is too large or too small, it will affect the gray balance and color reproduction.
The transparency of the ink is also very important, the transparency of the three primary inks must be more than 90% in order to better represent the intermediate color and discoloration. For example, in the past, the transparency of yellow was not good, at around 85%. At that time, the general printing sequence was yellow, yellow, blue and black. Yellow ink is the bottom, opacity is also not good, so no problem occurs. Recently, black, blue, yellow, and yellow ink are the last to print. When the transparency is not enough, the yellow version is heavy, and the ink layer is thicker, so that the entire screen is covered with a faint color.
In the packaging printing, often use the background color to highlight and highlight the theme, usually pink, orange, orange, orange, yellow, light blue, lake blue, grass green, light green, brown, brown, beige, snow, Light gray and other colors, which have an understanding of the color properties of the ink can be handy to obtain the desired color. The following points should be noted.
1 The color matching of ink is a subtractive effect, and the more the colors are, the darker and darker it is. Therefore, the color should be used as little as possible. First, it should be adjusted with two colors. After adjusting to a very close value, add a third color. Micro adjustments to achieve the desired color. Because the background color is often pale, the final rinse ink is added to lighten it. A small amount of flushing can be done first, and it is considered that the requirement is enlarged again, so as not to waste too much at once, especially after diluting, there is still a certain gap. Additions and adjustments, the more you work together, the more you work together, the more you fight, the more you exceed the amount you need. The color ink supplied by the ink factory has many intermediate colors and color changes in addition to the three primary color inks. When the ink is adjusted, two kinds of close color tones may be taken as necessary to achieve the requirement that the color tone is relatively clear and not too dark. Below there is a color ring diagram, arranged the name of the various inks, two kinds of colors close to the color of the mix more distinct, far away from the distance becomes gray. If you want to mix fresh grass green, you can use lemon yellow (yellowish) and green, when using yellow and medium blue, the emerald green is very dark.
2 When the color is washed with light, the color of the clear ink is dark, but it is not dark on the white paper. Diluting with white ink, the ink looks brighter but pink. Requests light color without pink and bright, and some people often add a small amount of white ink when using a large number of transparent dilute inks, although in the hue to achieve brighter requirements, but the white ink makes the ink with poor lightfastness easier to fade Disadvantages must be noted. Therefore, it is best not to add white ink when paper with good whiteness is light, and paper with poor whiteness is different.
3 The flesh color is also often diluted with gold and red ink, although the hue is good, but after the red light fades easily, it is not appropriate. Pink ink is also easy to fade after dilute. Diminishing the tone with darker 05-06 or darker 05-06, the fade is much better. When the yellow tone is not enough, the orange ink is slightly added. This ink is also good in light resistance and is not easy to fade. Light blue lake blue should be diluted with sky blue ink, do not use medium blue or dark blue, because it is easy to fade. Green ink and Qinglian ink have good lightfastness and lightfastness. They should also use lightfastness when lightening, otherwise they are easy to fade. The yellow ink is now lightfast than the sky blue ink and green ink, so when adjusting the green color should be considered in the future yellow will first fade, you need to pay attention to display the window packaging print.
4 Packaging printing sometimes uses aluminum foil or thin sheet metal. This often needs to consider the transparency of the ink in the background or pattern printing. The effect of the opaque yellow ink and the transparent yellow ink on the aluminum foil or iron sheet is completely different. A lot of candy-wrapped aluminum foil or tin box, first printed with a layer of transparent yellow ink, can make the metallic luster reflected through the yellow ink layer to become a golden color. The yellow ink with low transparency is very ineffective, and the use of high-transparency Taohong or magenta ink, sky blue ink, and green ink ink background color can make the aluminum foil or tin box show a very beautiful, vivid and bright color. Sometimes white ink is used to make the bottom, which is a complete requirement to cover the metallic luster of aluminum foil or iron sheet, and then print it like a pattern printed on white paper.
2. Fineness
The fineness of the ink is measured by a scraper fineness meter, which indicates how large the diameter of the largest solid particle in the ink is. Generally, the fineness of the letterpress ink is less than 20 microns, and the offset ink is less than 15 microns. This data is actually the diameter of a solid surface wrapped with a thick layer of oil. The diameter of a true solid is only half the size, ie, the relief base is less than 10 microns, and the offset ink is 7.5 microns or less. The so-called maximum particles account for a very small number of particles in the total solid particles of the ink, and most of the ink particles are much smaller. Even with the 15 micron count, the area of ​​the printed dot network is compared to the area of ​​the ink particles, or a dot can accommodate many ink particles. See Table 1 for details. The area of ​​the 250 lines listed in the table is also more than that of the 15 micron ink particles. The area is 6 times larger, and 40% is 23 times larger. Moreover, the vast majority of ink particles are much smaller than 15 microns. Therefore, the qualified factory ink will generally not affect the printing quality due to fineness problems.
A site survey was conducted on the problem of printing quality that affects the quality of printed matter due to poor printing ink quality. Except for a small amount of ink, the ink was thickened due to long-term storage of particles, or improper storage and use, and the surface of the ink was clogged. Most of the paper is deinked and mixed into the ink to cause ink thickening.
3. The rheology of ink
Offset or embossed inks are all sticky, thick paste-like bodies, which are physically called plastic fluids. They do not deform or flow like an ideal fluid (water) with external force. They must be added to a certain degree to start deformation. Or flow. As shown in Fig. 2, when the external force is applied, the ink does not flow, and the rheology that begins when the force reaches point A is added. The flow deformation at this time is a trend that is almost a solid movement and is called a plug flow. That is, the curve AC' in the figure indicates the relationship between force and rheology. When the force increases to C', the rheology of the ink flows like a perfect fluid in a laminar flow, and the rheological curve is linear. The force A that causes the ink to begin its rheology is called the minimum yield value, and the force C that causes the ink to start laminar flow is called the maximum yield value. The extension of the line above the C' point and the axis of force are changed to point B. The force at point B is called the ideal yield value. A preliminary understanding of the rheological properties of the ink's plastic fluid can be studied against the printing process's requirements for the ink's printability.
1viscosity, yield value and thixotropy and their determination
Relief and offset inks are viscous, thick plastic fluids. To determine the internal resistance of a flow, the so-called viscosity, first of all overcome the internal stress corresponding to the minimum yield value, so the Ford cup (paint cup) or falling ball The viscometer is not suitable. A peristaltic viscometer, drop bar viscometer, or parallel plate viscometer is typically used to determine the viscosity and yield value, or to characterize rheological curves to investigate its rheological and thixotropy properties.
â— Rotary viscometer
Commonly used are the Bruker Vist Viscometer and the Hermite Viscometer, the latter being used domestically. Its structure and principle is that the ink is placed in a small cylinder that can be kept warm. A rotor is inserted in the ink. When the rotor is rotated, the spring connecting the rotor is deflected by the viscosity of the ink, and the pointer is moved to directly read the viscosity. . By changing the cylinder and rotor and changing the rotation speed by the gearbox, the viscosity of various inks can be measured from 0 to 1.000.000 centipoise. The structural principle of the Bruker Vist Viscometer is basically the same as that of the Hermite Viscometer. However, it is possible to change a lot of speeds step by step, from the lowest speed step by step to the selected highest speed to determine a series of letterpress and offset inks. The data pairs for shear rate and shear stress will be depicted as an upwardly curved curve. A series of shear rate and shear stress data pairs are then determined as a straight line by stepping from the highest speed to the lowest speed. As shown in Figure 3. The size of the area surrounded by the two lines indicates the size of the touch. Actually, this is because the pigment particles in the ink attract and flocculate each other when they are at rest, so that they are in a thick condensed state. When the mechanical stirring force is applied, the flocculation force is destroyed and the thin and easily flowing state is achieved. But after a period of rest, it will flocculate again. This is the touch.
â— Drop stick viscometer (Raleigh viscometer)
The main structure is a horizontal short cylinder mounted on a vertical support, which is hollow and straight. A long round rod is inserted into the empty cylinder. The round rod and the cylinder have a certain gap. The ink is added in a certain amount in the gap, so that the round rod and the round The middle of the barrel is filled with ink, and weights of different weights are placed on the round bars. Determine the time required for the free fall of the round bar by 10 cm. Due to the resistance of the viscosity of the thin layer ink when the round bar falls, and because of the different weights on the round bar, different times are required to express the shear rate of the ink, and the ink flow curve can be plotted and calculated accordingly. Theoretical yield value and plastic viscosity.
â—Parallel plate viscometer
A certain amount of ink is placed between the two flat plates placed horizontally. The upper plate has a prescribed weight and can be freely dropped horizontally at a fixed height and pressed against the ink. The ink is circularly arranged in two parallel directions. The middle of the board is expanded. The diameter of the ink spread increases with time, and the diameter of the ink spread is recorded at different times of 10 seconds, 60 seconds, 100 seconds, etc., and the slope, intercept, and yield value of the ink rheological curve can be calculated.
2 stickiness and its determination
When the ink is run on the ink roller of the printing machine, it is torn by the ink roller that rotates in the opposite direction. The resistance generated at this time is called the viscosity of the ink. This is the comprehensive force that the ink's cohesion and adhesion are balanced with each other. Performance. Unlike the viscosity of the above ink, there is no absolute unit. The viscous index is measured with an ink gauge (ink stickiness meter). Its main structure is the three ink rollers and the connected weights and balances. When a certain amount of ink runs between three ink rollers at a certain temperature, the ink layer is The resistance of tearing is transmitted to the balance bar, and a viscous reading is obtained with the weight hit. The use of tack to study the transfer of inks on printing presses is more practical than viscosity, and has therefore been valued by the ink and printing industry in the world.
3 fluidity and its determination
0.1 ml of the ink was subjected to a total weight of 250 g in a round glass sheet having a diameter of approximately 70 mm at a temperature of 25°C. After 15 minutes, the ink was flattened to expand into a circular diameter of mm. This is a comprehensive representation of the thickness, soft and hard viscosity, and yield value of the ink.
4The relationship between various rheological properties and printing adaptability of ink
Because letterpress and flexographic printing inks are plastic fluids with more complex rheological properties, the structure and properties of various printing presses have different requirements for inks. Therefore, the relationship between the rheology of these various inks and printing suitability It is also related to each other and is very complicated. We can only give a rough introduction here.
Viscosity for letterpress and offset inks is not as obvious and strictly related to printing as for flexographic inks and gravure inks, but there is a general rule that the printing speed is slow, and higher viscosity inks can be used; the printing speed is high. The ink used has a lower viscosity. Such as the wheel transfer ink is much smaller than the ink viscosity. Offset inks used in high-speed four-color offset presses are less viscous than offset inks used in general-purpose monochrome or two-color offset presses. However, the viscosity of the ink becomes smaller as the temperature increases. After the high-speed offset printing machine is opened, the ink roller has a high speed and a high temperature rise, the viscosity of the ink will gradually become smaller, so the viscosity is slightly higher, and the substrate has a relationship with the viscosity of the ink. The smooth and solid paper can be used at a high level. Viscosity of the ink, the structure of loose paper on the use of smaller viscosity ink, otherwise it is easy to fall powder, hair removal.
Viscosity and viscosity are related, that is, the viscosity of the ink with large viscosity is generally high. However, there are also irrelevant times, so some inks have similar viscosity but different viscosities. Some inks have similar viscosities and different viscosities. In this case, the ink should be selected mainly for stickiness. For example, the color offset ink has a viscosity in the range of 5-9. The applicable range of the color printing ink viscosity is 5-11. The offset printing ink has a much faster printing speed and the applicable adhesive range is 3-6. The viscosity of the ink has a great relationship with the printing speed, the separation speed of the ink layer at the printing speed is also fast, and the viscosity exhibited by the ink is also large, which is the main reason why the offset of the offset printing ink is particularly low. Viscosity has a great influence on ink transfer and ink distribution. In the applicable range, inks with higher viscosity are better for ink transfer. The ink layer printed on paper is also thicker and the dots are more realistic. However, when the viscosity is too large, unevenness occurs on the ink roller or even the roller stacker or the stacker rubber. At this time, the dots of the print are also hairy and false. When the viscosity is too small, the ink transfer is poor, and the ink layer printed on the paper is thin at the end, and it is easy to expand the dots. The viscosity of the ink is very much related to the paper. For example, the same sticky ink is printed on the offset printing machine. The relatively solid imported coated paper can be printed well. Switching to the poorer coated paper produced by China will cause the powder to fall off and even peel off. It is the paper that cannot withstand the stickiness of the ink layer as it separates between the eraser and the paper. Viscosity is related to temperature. When the temperature is high, the viscosity is lowered. The offset printing machine pauses during the printing and then meets to cause the paper to lose skin. The reason is that the car has cooled for a while and the viscosity of the ink has increased. First print some good paper waste paper, the car will be normal after a period of time. In a four- or more-color offset press, the mutual stickiness of the four colors is also important. In general, the viscosity of the latter color ink cannot be greater than the previous color, otherwise it will pull down the previous color ink on the print.
The yield value and fluidity are related to the "body bone" of the ink. The so-called "body bone" ink is often a large yield value, and the ink surface with a large yield value looks harder on the ink body, and the ink is run on the ink roller. Shorter, less fluidity measured. In the proper range, the ink with the smaller yield value and greater fluidity is more suitable for printing on the embossing or offset printing machine. Due to the short drawing speed, less ink flying phenomenon, the harder fluidity of the ink body, and the smaller dot on the printing product thick. When it is too large and out of range, poor ink transfer is caused, unevenness is caused on the ink roller, and sometimes the ink is not discharged in the ink fountain.
The thixotropy of the ink is too large, due to the flocculating nature of the pigment particles, it can stop the ink from flowing for a short period of time due to flocculation. This is often due to the fact that the embossing and offset ink fountains do not release ink, resulting in the prints becoming more and more faded. The main reason. However, in the thixotropic inks, the printed dots are thicker, so it is not as small as possible. As to whether the scope of large or small is more appropriate, the general ink industry has not published any data.
4. Fixation and drying of ink
After the resin ink is printed on the paper, the low-viscosity solvent and dry vegetable oil can quickly penetrate into the pores of the surface of the paper, so that the synthetic resin and the dry vegetable oil remain on the surface of the paper and solidify. This state is called dryness. solid. At this time, a small amount of printing pressure on the back side will not stick on the back side, but the pressure will be too sticky. The solid ink layer is further oxidatively polymerized to form a firm film, which is truly dry. Generally, the resin ink has two stages of fixing and completely drying. The fast fixing ink is called fast fixing. The fixation is actually measured in seconds, but it is based on the test method and the instrument. The dryness is comparable to the time when the print is completely dry, in hours.
Fast fixing of the ink on coated paper or coated paper is remarkable because the pores on the surface of the coating are very fine and numerous. You can inhale an appropriate amount of solvent in a very short time and it is in a fixed state. The voids on the surface of a general offset paper are coarse and small, and a certain amount of solvent cannot be taken in a short time to fix the ink, so the effect is not good. The fixing state of the ink is not really dry, so only a small number of printing parts can be stacked and can not be moved by hand because the stacking excessive pressure is too large, or the local compression is too large by the hand-moving, only the fixing state The ink layer will still be damaged and make the back stick. The ink printed on the paper, whether fixed or not, due to the oxygen in the air, the unsaturated double bond of the dry vegetable oil acts, first the oxygen, then the polymerization, gradually increase the molecular weight and finally become a firm film, this is the real dry. Therefore, the conditions for the ink drying are the oxygen in the air and the heat or chemical accelerator that causes or promotes the oxidative polymerization, that is, the drying oil.
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