Precautions for the use of solvent-based inks
01
Solvent-based inks are dangerous goods and should be stored away from fire sources. Printing factories mostly store them in the basement or the dangerous goods warehouse with low temperature, in this case the viscosity of the ink is on the high side, and when the storage temperature is lower than 0 ℃, the ink will also happen the phenomenon of gelation. When the ink from the low-temperature warehouse out, can not be immediately poured into the ink tank to use, otherwise the performance of the ink can not be played normally, affecting the quality of printed matter. At this time, the ink should be warmed up before use, but also pay attention to the temperature should not be too fast, to prevent the solvent volatilisation ratio is out of proportion and affect the performance of the ink. It can be stored under the same condition with the temperature of printing workshop for one day and night before use.
02
Solvent ink should be stirred well before use, because there will be some pigment precipitation after long time storage, resulting in inconsistency of pigment content in the upper and lower parts of the ink, which will affect the consistency of the hue before and after the printed matter.
03
The initial viscosity of solvent-based ink produced by the ink factory is generally high, mostly in 30-40 seconds, up to 60 seconds. Before printing on the machine should be used to reduce the viscosity of the ink with the appropriate diluent, and viscosity control in about 25 seconds (25 ℃ * coated 4 # cup). Control viscosity to not dry plate, no false edges, no roughness for the upper limit of viscosity, to the prints are not watery, the colour is not thin for the lower limit of viscosity.
At the same time, attention should also be paid to the selection of the same type of ink used with the diluent. Various types of solvent-based inks are equipped with special diluents, because of its composition is different, so it must not be added at random, so as not to affect the ink, can not be normal printing.
In addition, the choice of thinner should be combined with the printing speed, dryer temperature, seasonal and other factors. Solvent-based plastic film printing ink, for example, the general situation can not be used in normal (medium-speed) diluent, summer can be added to the appropriate amount (less than 5%) n-butanol to reduce the drying speed, the winter can be used to fast diluent.
04
In printing, due to the solvent-based ink in the colour, continuous material, solvent to the substrate on the transfer of different properties, after a period of time, due to the reduction of resin content in the ink, solvent evaporation, the ink becomes viscous, the need to add thinner to adjust, but to control the amount of thinner. If the printing machine is not installed on the ink circulation system, when adding thinner should not be added too much at a time, we should use a small amount, add diligently, while adding the method of stirring, in order to maintain uniformity and consistency of ink, to prevent changes in the ink structure. Moreover, after adding several times of thinner, it is necessary to add a part of the original ink appropriately, in order to ensure the consistency of the colour and gloss of the printed matter.
05
In the printing process, due to the substrate surface coating off (especially paper materials), it is easy to fall into the ink, resulting in larger ink particles. Tested and found that the fineness of the ink will increase by more than 50цm from the original 20цm. These impurities are prone to cause knife lines, white spots and other printing faults, so the ink circulation system should be strengthened printing machine ink filtration, get rid of impurities.
06
Different types of ink can not be mixed and blended with each other, so as not to trigger ink deterioration. In particular, it is necessary to prevent the misuse of gravure printing ink mixed with flexographic printing ink, affecting the printing quality.
07
The remaining ink after printing is completed is stored in a sealed container after being filtered, and can be mixed with the same variety and colour for use in the next printing.
08
Solvent-based ink is dried by volatilisation, and the volatilisation rate of solvents by the environmental temperature and humidity, and the relative humidity is too low will produce static electricity. Therefore, the printing environment is best to maintain a constant temperature and humidity, the general temperature control at 25 ℃ ± 1 ℃, the relative humidity control at 65 ℃ ± 5%, in order to reduce printing failures.
09
Most solvents are flammable, explosive, and have a certain degree of toxicity, polluting the environment and endangering personal health. Therefore, production, use and storage should pay attention to fire prevention, explosion-proof, while as far as possible to use non-toxic or low-toxicity solvents, solvent recovery devices to deal with, in order to reduce environmental pollution.
Gravure printing common failure analysis
1, poor print fastness
Causes and solutions:
(1) PE or PP film surface tension is lower than (3.6-3.8 × 10-2N/m). Surface tension measuring fluid to check the surface tension of the film, if not up to the requirements, should be re-processed.
(2) The ink is diluted too thin, the binder is destroyed or the wrong diluent is used. When diluting ink viscosity is best controlled at 25-35 seconds (coated 4 # cup) is appropriate. In addition, the choice of thinner should be carefully, do not use the wrong, so as not to affect the quality of the ink.
(3) The ink itself has poor adhesion fastness to the film. Ink varieties should be replaced or ink manufacturer contact.
2, the print is lost
Phenomenon: in the printing process, the beginning of the small words, fine lines lost, and in severe cases, can not print the pattern.
Causes and solutions:
(1) ink viscosity is high, and printing speed does not match. Adjust the ink viscosity is not to the right value.
(2) ink drying speed is too fast, while the printing speed is too slow. Ink in the slow drying diluent (or n-butanol slow drying solvent), but to strictly control the amount added, such as adding too much will occur, such as adhesion and other ills.
(3) Printing plate mesh is too shallow, the need to re-make the plate.
(4) scraper angle and position is not appropriate. Normal doctor blade angle is generally between 30-60 °, not only can keep the blade is not easy to hurt the plate, and printing ink layer is better. Squeegee position should be combined with the ink drying situation, such as ink drying too fast, the squeegee can be moved forward appropriately, shorten the distance between the squeegee and the embossing point.
(5) to the hot air position is not appropriate, adjust the hot air position.
3, overflow ink
Phenomenon: field printing surface with spots, patterns, or ink overflow from the line part.
Causes and solutions:
(1) low viscosity after ink dilution. Add part of the original ink, the viscosity will be adjusted 25-35 seconds (the current task 4 # cup); or empty machine printing for a period of time, so that the solvent volatilised off part of the ink viscosity to increase to a suitable value.
(2) Printing speed is too slow, or the ink drying speed is slow, improve the printing speed, or to the ink to adjust the drying thinner.
(3) The printing plate screen cavity engraving is too deep or wear and tear is serious, need to re-make the plate.
(4) Squeegee hardness, pressure and angle is not appropriate. Adjust the squeegee pressure and angle, grinding squeegee knife edge, reduce the hardness.
4, eat colour
Phenomenon: set printing, the ink on the plate of the latter colour will be printed on the substrate before the ink of the colour of the prints stick down, reverse print to the plate of the latter colour.
Causes and solutions:
(1) The thorough drying of the ink of the previous colour is not good. The former colour ink to add fast-drying diluent, improve its drying speed, and make the latter colour ink slower than the former colour ink.
(2) The previous colour ink adhesion fastness is not good, replace the ink.
(3) Printing speed is too fast, the printing plate mesh cavity engraving is too deep, the printing pressure is too large, reduce the printing speed, strengthen the drying function, reduce the pressure of the printing rollers or change to a shallow plate.
(4) improper use of thinner, check and change the appropriate thinner.
5, adhesion
Adhesion phenomenon can be broadly divided into three cases.
(1) after the print reel to the bag when the adhesion occurs, known as ‘a sticking’.
(2) after the storage of the bag in the packaging of goods, plastic bags in the bundle of adhesion phenomenon, known as ‘secondary adhesion’.
(3) The adhesion that occurs after packaging is called ‘three adhesion’.
Causes and solutions:
Generally speaking, the main factors causing adhesion are pressure, temperature, relative humidity and time.
A sticking is mainly due to residual solvent in the print or winding tension. This is due to the ink thinner volatilisation is too slow or printing speed is too fast, while the drying system drying effect is poor, the printing plate mesh cavity engraving is too deep, the ambient temperature and humidity is too high. As long as the selection of appropriate ink thinner, reduce the printing speed, enhance the drying effect of the drying system, improve the ambient temperature and humidity, properly reduce the winding tension, re-production of shallow mesh plate cylinder and other measures, can be solved and avoid the problem of primary adhesion.
Secondary adhesion is mainly affected by the temperature and humidity of the product storage environment, mainly the ambient temperature or relative humidity is too high, so that the ink becomes soft, sticky or resorption occurs, thus causing adhesion. Such as ink under normal circumstances can withstand 50 ℃ temperature, but when the relative humidity increased by 10%, its heat resistance will decline, only 45 ℃. For this reason, as long as the control of environmental temperature and humidity, the general secondary adhesion can be prevented.
The third adhesion is mainly caused by the contents. Due to PE, PP film has permeability, when used to package items containing alcohol, esters, flavours, etc., such as balsam, liquid cosmetics, ginger, mustard, curry powder, etc., it will be due to alcohol, esters, flavours, etc., exuded and migrated to the ink layer, so that the ink layer of the resorption of the adhesion occurs.
6, whitening
Phenomenon: a layer of white box on the surface of the print.
原因
(1) solvent whitening: mainly because of the ink used in the volatile latent heat of solvents, such as alcohol solvents, when the environmental relative humidity is too large, the solvent excavation in the imprint caused by the imprint of the ink layer of the temperature drop in the air pooling of moisture falls to the surface of the imprint, thus forming a layer of white frost.
(2) resin whitening: due to the ink solvent volatilisation rate is different, so that the solvent is out of balance, mainly true solvent volatilisation rate is faster than the volatilisation rate of the diluent, and thus the proportion of the ink accounted for by the diluent increases, and when increased to a certain extent, will cause the resin to precipitate, thereby forming a layer of material similar to the white frost.
Solution:
(1) Reduce the relative humidity of the environment, it is best to be able to maintain a constant temperature, constant humidity printing conditions.
(2) Enhance the drying effect of the drying system.
(3) Change to slow drying solvent.
(4) Add some slow evaporation rate of the real solvent, or adjust the ratio of solvents.
7, water lines or water splash
Phenomenon: the field part of the print is not full, there are wavy patterns.
Produce causes and solutions:
(1) ink viscosity is low. Supplement the appropriate original ink, or add high viscosity continuous material.
(2) slow printing speed. Appropriate increase in printing speed can be.
8, ring-shaped mottling
Phenomenon: the print is not flat, the field part of the irregular mottling.
Causes and solutions:
(1) ink thixotropy, poor levelling, or excessive ink dilution, low viscosity, should replace the ink or improve the viscosity of the ink.
(2) drying speed is too fast, printing speed is too slow. Add slow drying diluent, adjust the printing speed.
(3) The printing plate mesh hole is not appropriate (generally deep), need to re-engrave the plate.
(4) The effect of static electricity. Increase the device to eliminate static electricity, or add antistatic agent in the ink.
9, bubble
Phenomenon: tiny bubbles in the ink, the print appears blank dots.
Causes and solutions:
(1) There is a large amount of air mixed in the ink tank. Use defoamer to reduce the amount of air bubbles.
(2) The drop when the ink returns to the ink tank is too large. Adjust the position and height of the ink tank.
(3) The ink has been stored for too long. Adjust and add some new ink or replace all.
(4) Printing speed is too fast. Appropriately reduce the printing speed.
10, blocking plate
Phenomenon: ink in the printing plate mesh hole dry solid, resulting in printed text, lines missing or disconnected, serious patterns can not be printed.
Causes and solutions:
(1) the distance between the squeegee contact point and the embossing point is large. Shorten the distance between the squeegee contact point and the embossing point.
(2) Printing speed is slow. Increase the printing speed.
(3) Ink dries too fast, in the screen cavity of the printing plate before it is transferred to the substrate. Add a slow drying agent to the ink to reduce the ink drying speed.
(4) Ink particles are too large or mixed with other impurities. Filter the ink or replace the ink.
(5) The printing plate is not cleaned, and the residual ink dries and solidifies in the mesh cavities, causing blockage. Thoroughly clean the printing plate.
11, the ink is jelly-like
There are two cases, one is just pulled out of the warehouse ink is jelly-like, can not be poured out of the ink drum. Generally easy to occur in the winter and spring this phenomenon, which is due to the ink in the continuous material of low temperature resistance caused by poor. If the ink jelly is light, gently shake the ink drum can destroy this property, and then can be used on the machine. If the ink is heavy jelly, it should be stored in the room temperature environment for a day and night, until the ink back to normal before use.
Another situation is in the process of use, the fluidity of the ink gradually deteriorate, until it is jelly-like and can not flow, which is mainly due to the improper use of diluent (such as only alcohol or stupid) and caused by the alcohol may also be too high water content. When the relative humidity of the environment is too high, due to the hygroscopic effect of the alcohol in the ink, over time, the increase in moisture in the ink, resulting in poor ink flow or even jelly-like. This situation is rare, you can re-exchange the ink, the new ink can be added to a small amount of frozen ink to use. In order to prevent this from happening, each time the ink should be added less thinner, and to add some of the new ink at the same time, in order to ensure the stability of the ink composition.
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