In gravure printing, the quality of the ink is one of the important factors affecting the quality of the printed product. Facing the numerous inks supplied by ink manufacturers, how to select the high quality inks suitable for their own products is a profitable issue that cannot be ignored for the printing operators.
In order to print a print that meets the requirements, the ink must have certain properties. It mainly includes color, viscosity, thixotropy, adhesion, viscoelasticity, dryness, fineness, tinting strength and various resistances. It is not possible for a printer to make a full test. The author after years of practice believes that the ink to be purchased can focus on the following four aspects of routine testing.
The quality requirements of color prints require that the color difference of the same color is small, so the detection of color is very important. The color detection can be performed in the following steps.
(1) Use a small-tuned ink-jet knife to sample a small amount of the ink (standard sample) and the ink to be tested (sample), place them on a glass plate, and mix them thoroughly.
(2) Use a small dobby knife to take a small sample and apply it to the upper left of the scratch paper. The positions of the two should be adjacent and not connected.
(3) Using a spatula to force the two inks from the top down to a thin layer on the paper. When scraping to a depth of about 5 cm below the black line, the spatula is gradually leveled off while reducing the force so that the ink forms a thicker ink layer on the paper. Cover a small piece of cellophane over a thick layer of ink to avoid smudging.
(4) Visually observe the differences in the background color, face color, and ink color between the standard sample and the sample. When judging the background color, the scraping paper should be back to the light source, and the color to be observed through the perspective method. Face color refers to the color of the ink under normal conditions. Ink refers to the color of a pile of ink.
The length of the silk ink head refers to the so-called silk head of the ink. For example, open a bucket of purchased ink, stir it evenly with an ink dipstick, and then use a knife to pick up the ink. The ink flows downwards and draws the filaments. If the ink flows down from the knife, its filaments continue to be called long. Filament long inks When the flowing filament breaks, filament retraction occurs. If the ink flows down from the knife, the disconnection is quicker and the filaments are intermittent, and the filament is called short. With a short head of ink, when the flowing filament breaks, the shrinkage of the filament is much lighter than that of the silk head. In the printing process, generally speaking, the long ink of the silk head has good ink under the ink, and the ink with the short silk head has poor fluidity in the ink fountain, the ink is not good, and the distribution on the plate is also poor. However, the filament should not be too long, otherwise the separated filaments will form a mist and cause the "flying color".
The fineness of the fineness of the ink indicates the size of the particles of the pigment (including the filler) and the uniformity of the distribution of the particles in the web. Fineness has a great influence on the printing quality, especially for gravure printing, if the fineness of the ink is poor, it is easy to produce emptiness, expansion or occurrence of paste version and other phenomena. Fineness can be measured with a fineness meter. The specific detection method is as follows:
(1) Take a small amount of ink to be tested, dilute it to the appropriate concentration, and place it in the deepest part of the groove of the fineness meter.
(2) Use a spatula to move from the deepest point of the groove to the shallowest part. When the ink fills the groove, observe the position of the dense particles and read the density values ​​from the scales on both sides of the groove. The fineness of general ink should be within 25μm to be qualified.
In the printing process, the fineness of the ink is generally judged roughly by the naked eye. The specific method is to drop the ink on a smooth paper surface and use a ink knife to scratch the ink. If the surface of the ink is smooth and even, the fineness is good. If the surface of the ink is rough and there are obvious traces of the particles, the fineness is poor.
Viscosity inks are viscous fluids that have internal friction when flowing. The magnitude of this resistance can be expressed in terms of viscosity. It is very important that the viscosity of the car is measured by the printing operator. For example, inks purchased at the same price will be economical to use when the other qualities are the same.
The measurement of the viscosity must be carried out at a specific temperature, otherwise no correct measurement result can be obtained. This is because the viscosity of the ink changes with temperature. Generally, the temperature of the ink is controlled at 25°C. The specific measurement method is as follows:
(1) Mix and adjust the ink to be tested, and use a beaker to take a certain amount of ink for heating (usually heated with hot water, it is forbidden to directly heat the fire) until the temperature of the ink reaches 25°C.
(2) Place an outflow viscometer (in this case, 4# coating cups are used for usage) on the adjusted iron stand.
(3) Pour the ink in the beaker into the bottom hole of the No. 4 coating cup meter. When it is full, remove the finger and start timing until the ink has run out. The general viscosity should be 40-60 seconds.
In actual production, in addition to the several routine tests mentioned above, we must combine certain characteristics of the product and the surrounding environment, and then carefully test it from other aspects to achieve targeted, specific analysis of specific issues, and strive to buy for themselves Ink.
In order to print a print that meets the requirements, the ink must have certain properties. It mainly includes color, viscosity, thixotropy, adhesion, viscoelasticity, dryness, fineness, tinting strength and various resistances. It is not possible for a printer to make a full test. The author after years of practice believes that the ink to be purchased can focus on the following four aspects of routine testing.
The quality requirements of color prints require that the color difference of the same color is small, so the detection of color is very important. The color detection can be performed in the following steps.
(1) Use a small-tuned ink-jet knife to sample a small amount of the ink (standard sample) and the ink to be tested (sample), place them on a glass plate, and mix them thoroughly.
(2) Use a small dobby knife to take a small sample and apply it to the upper left of the scratch paper. The positions of the two should be adjacent and not connected.
(3) Using a spatula to force the two inks from the top down to a thin layer on the paper. When scraping to a depth of about 5 cm below the black line, the spatula is gradually leveled off while reducing the force so that the ink forms a thicker ink layer on the paper. Cover a small piece of cellophane over a thick layer of ink to avoid smudging.
(4) Visually observe the differences in the background color, face color, and ink color between the standard sample and the sample. When judging the background color, the scraping paper should be back to the light source, and the color to be observed through the perspective method. Face color refers to the color of the ink under normal conditions. Ink refers to the color of a pile of ink.
The length of the silk ink head refers to the so-called silk head of the ink. For example, open a bucket of purchased ink, stir it evenly with an ink dipstick, and then use a knife to pick up the ink. The ink flows downwards and draws the filaments. If the ink flows down from the knife, its filaments continue to be called long. Filament long inks When the flowing filament breaks, filament retraction occurs. If the ink flows down from the knife, the disconnection is quicker and the filaments are intermittent, and the filament is called short. With a short head of ink, when the flowing filament breaks, the shrinkage of the filament is much lighter than that of the silk head. In the printing process, generally speaking, the long ink of the silk head has good ink under the ink, and the ink with the short silk head has poor fluidity in the ink fountain, the ink is not good, and the distribution on the plate is also poor. However, the filament should not be too long, otherwise the separated filaments will form a mist and cause the "flying color".
The fineness of the fineness of the ink indicates the size of the particles of the pigment (including the filler) and the uniformity of the distribution of the particles in the web. Fineness has a great influence on the printing quality, especially for gravure printing, if the fineness of the ink is poor, it is easy to produce emptiness, expansion or occurrence of paste version and other phenomena. Fineness can be measured with a fineness meter. The specific detection method is as follows:
(1) Take a small amount of ink to be tested, dilute it to the appropriate concentration, and place it in the deepest part of the groove of the fineness meter.
(2) Use a spatula to move from the deepest point of the groove to the shallowest part. When the ink fills the groove, observe the position of the dense particles and read the density values ​​from the scales on both sides of the groove. The fineness of general ink should be within 25μm to be qualified.
In the printing process, the fineness of the ink is generally judged roughly by the naked eye. The specific method is to drop the ink on a smooth paper surface and use a ink knife to scratch the ink. If the surface of the ink is smooth and even, the fineness is good. If the surface of the ink is rough and there are obvious traces of the particles, the fineness is poor.
Viscosity inks are viscous fluids that have internal friction when flowing. The magnitude of this resistance can be expressed in terms of viscosity. It is very important that the viscosity of the car is measured by the printing operator. For example, inks purchased at the same price will be economical to use when the other qualities are the same.
The measurement of the viscosity must be carried out at a specific temperature, otherwise no correct measurement result can be obtained. This is because the viscosity of the ink changes with temperature. Generally, the temperature of the ink is controlled at 25°C. The specific measurement method is as follows:
(1) Mix and adjust the ink to be tested, and use a beaker to take a certain amount of ink for heating (usually heated with hot water, it is forbidden to directly heat the fire) until the temperature of the ink reaches 25°C.
(2) Place an outflow viscometer (in this case, 4# coating cups are used for usage) on the adjusted iron stand.
(3) Pour the ink in the beaker into the bottom hole of the No. 4 coating cup meter. When it is full, remove the finger and start timing until the ink has run out. The general viscosity should be 40-60 seconds.
In actual production, in addition to the several routine tests mentioned above, we must combine certain characteristics of the product and the surrounding environment, and then carefully test it from other aspects to achieve targeted, specific analysis of specific issues, and strive to buy for themselves Ink.
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