The secret of the correct use of water-based ink
1. The characteristics of water-based ink:
(1) Slow drying effect on printing quality: general of water-based ink can be divided into two types, one is alcohol (> 10%), one is less do not contain alcohol or alcohol (< 10%).No matter what kind of products, in view of solvent-based inks, has been slow to dry ink.Slow dry ink in water, can cause great difficulty to dry ink, printing quality is easy to cause flow (water), after tack, unequal transfer problem.In general, in ink, the higher the content of ethanol, the more likely the problem little except (isopropyl alcohol).
(2) Transfer rate influence to printing quality: with ink, different solid content, ink transfer rate is not the same.Put a blossoming smile (filling) material, in terms of resin, the content is different, transfer rate is also different.High resin content (> 30%), the light version of the transfer rate is high;Low resin content (< 25%), deep version of high transfer rate.How to do a high-profile to low-key version (dark color) transition, this is the problem of water-based ink.Otherwise, due to the uneven transfer rate, it is difficult to print out hierarchical effect.
(3) The solubility influence to printing quality: in water-based ink, water is not a true solvent, that is to say, water cannot be separate to dissolve resin.So-called water-based ink, in which water is not the continuation of the continuous phase and dispersed phase is not continuous.For this reason, when adding water ink, you need the assistance of other factors, can make water evenly dispersed in the ink.The use of water-based ink, cannot like solvent ink, can be arbitrarily add diluent.Otherwise you can be sure that transfer printing quality will be uneven, show color uneven, dispersion phenomenon such as bad.
(4) Covering rate influence to printing quality: due to reasons of water-based ink use resin, pigments, the color is often more transparent.This is the problem of insufficient cover rate.Adopt the method of enhancing the pigment content, can solve part of the problem, but also a large negative effects, such as high viscosity, thixotropy.Printing enterprise, therefore, cover rate high demand, if any, shall be made to the system of ink factory.
2. The standardization of water-based ink printing assignment:
(1) The prepress work elements: prepress work is very important, is the important factor of printing quality is good or bad.
①Ink: unlike solvent ink, water-based ink dilution method such as solvent ink, not can be large, one-time to join thinner.Because water is not a true solvent for resins, when diluted should pay attention to two points: one is unfavorable printing while dilution;One is not a one-time joining more than 8% of the diluent.Standard way is: to determine the drying conditions (> 55 ℃), determine the printing speed (such as 40 m/min), determine the depth of the plate (e.g., 35 microns), diluted 5% for the first time in the barrels of water, stirring after 10 minutes, and then dilute stir, 5% of the water, 10 minutes, can prepare computer printing.At this time of the printing viscosity should be adjusted in 18 ~ 20 s advisable.If need to adjust the viscosity in ink barrels to dilute 5% ~ 10% of the water, methods such as before.
② Adjust the scraper: vice knife is a knife in the distance adjustment to 0.3 cm is more appropriate.A knife Angle setting of 60 to 120 degrees (according to the actual confirmation).
③ Diluent, thinner, the adjustment is very important, not careless.The most basic is to adjust the pH of the water (9) to the appropriate scope, if possible, adjust the tension of water is also good.This is good for printing.A lot of people thought that so long as the water, it is unscientific.Thinner, the adjustment of the formula, it should be adjusted, according to the requirement of the printing ink manufacturers to be targeted.
④ Thin film: material requirements smooth, uniform thickness, there can be no folding material, die mark, corona requirements above 38 dyne.
(2) The elements of work in print: water-based ink in the printing process operation, it is very convenient.To make the print quality is stable, pay attention to three aspects.
① The stability of the pH: general water-based ink for pH requirement between 8 ~ 9.5.Considering making ink manufacturers that dry, water resistant, cost factors, such as pH balance agent is often used by quick volatile substances.It's easy to cause the change of pH value, so be sure to focus on in the process of using pH changes.Printing factory should purchase the corresponding equipment, such as pH value test pen, the ink in the ink tank track.PH value is not stable, directly affect the quality of the printing quality stability.
② Of the water-based ink viscosity adjustment: in front of the computer printing, has been adjusted on the ink viscosity, but in the process of printing, has yet to be tracking the ink viscosity changes, such as water to adjust viscosity, disposable water to no more than 5%, best can in a ratio of 3:7 (alcohol, water).We tend to make the empirical mistake, the way to use ink on the use of solvent-based inks, one-time to join a lot of diluent, dosage is not accurate measurement, it is unscientific.Adjust the viscosity of water-based ink observation, adjust the 4 hours.As long as the complete control of pH value, viscosity, water-based ink printing quality relative will be stable.
③ The adjustment of the pressure rod: PE film pressure slightly larger, the rest depends on the equipment situation.The faster the printing speed, pressure slightly larger.
④ Winding, winding Zhang Liyi loose not tight, cannot too big, that is to say, tension winding diameter cannot too big, not more than 55 cm diameter range.
⑤ Plate and ink tank: if need downtime when printing, plate from the ink tank can't be too long, because of the water-based ink resin is often can't dissolve, that is fundamentally different with solvent ink.
⑥ Scraper cleaning: 8 hours cleaning once, can operate on the machine.Required to prepare material in print: pH pen/viscosity cup (# 3)/move light oil/ethanol/paste/measuring cup (10, 50, 100, 500, 1000 l).
(3) After printing work elements:
① False detection: dry because of the water-based ink using ammonia as a pH regulator, and in the process of dry evaporate, ammonia is impossible to completely evaporate, about 30 to 40% of the ammonia still remain in the ink layer.The ammonia material in the ink layer is 0.3, it is easy to appear "false phenomenon", this material will cause bad influence to printing quality after printing, reflect the most prominent is the "return".The effective method to solve this problem is the print off the plane after 70 ℃ drying for 1 hour.
② The adhesion test: random instant qualifying examination (adhesion area of 90%) - 12 hours test (adhesion area of 100%)
③ Water resistance test: 1 hour test (wet wipe out 10 times the ink) - 24 hours test (20 times not to drop the ink wet wipe) -- seven days test (30 wet wipe out ink).Or the test according to the requirements.
④ Other detection.Water-based ink performance reflects the period normally for 7 days.A solvent ink.
3. The requirement for plate: plate depth is set to between 25 ~ 35 ц m.Hardness greater than 800.Version to the basic requirements are:
(1) Version of the deep between 15 to 25 microns: 150 ~ 150 mesh, Angle of 45 degrees cylindrical version.
(2) Version of the deep between 25 ~ 35 microns: the network of 90 ~ 110 mesh, Angle of 45 degrees cylindrical version.
(3) Ink fineness between 10 ~ 15 microns, appropriate use of network is greater than 170 mesh version;Ink fineness between 5 ~ 10 microns, and appropriate use of network for more than 190 mesh.
(4) Gravure adjustable ratio: due to the slow drying, low viscosity, water-based ink, gravure mesh point of ink is hardly dry, high-profile transfer of parts is better, so the dark parts of the transfer, poor level of contrast tend to weaken.The solution is to should be adjusted net hole in the middle of the depth, make the version in the middle of the transferred to the highlights of the net hole depth, in general, a solvent.
4. Printing faults and solution:
(1) Fog and paste version:
Reason: in the high speed printing, water-based inks are prone to fog and paste version, this is because the aqueous film evaporation drying slow, attached to the gravure roller on the surface of the membrane layer is easy to transfer to the substrates, and is mixed with the powder in the ink tank, or insolubles caused by the precipitation of resin, increases the resistance of scraper, scraper can't scrape board.Solution: filter ink, add the appropriate pH balance agent, increase the squeegee pressure (try not to use), improved version of the production of precision.
(2) Resin precipitation: reason: dilute too, pH imbalance, join the wrong thinner.Solution: adjust pH value, filter the ink.
(3) Slow drying: reason: high viscosity, oven temperature, the wind.Solution: reduce viscosity, enhance oven temperature and wind.Note: such as four-color overprint, water-based ink drying speed is 4 ~ 5 times of solvent ink.Use water-based ink, printing plate depth of 20 microns drying speed and the use of solvent ink, version deeply 38 microns of drying speed is basically the same.
(4) The water ripples: reason: low dilution overdo, viscosity, film printing speed too slow, uneven.Solution: appropriate adding resin, printing ink, printing speed.