Waterborne Varnish Problems

First, the experimental method of abrasion resistance Print anti-wear test is one of the basic experiments commonly used by packaging and printing companies. There are many ways to detect anti-wear, I, raw, and there are different ways to illustrate the anti-wear effect. When I visited a folding carton printing factory recently, I found that they only used a white paper strip to gently wipe the surface of the printed product. The final anti-wear effect was based on whether the ink was transferred to white paper. For this unscientific experiment method, my evaluation is: The printing factory adds many additives that can reduce the friction coefficient in the coating formulation in order to obtain good abrasion resistance, but this only increases the smoothness of the surface, actually It will not really improve the anti-wear properties of the ink film.
In addition, I also learned several ways to test the abrasion resistance, but it is not reliable, because the final judgment of the abrasion resistance of these experimental methods is based on only one experiment. In fact, the final judgment of the anti-wear effect should be taken from the printed matter for a number of samples to be tested and the final composite value taken. If necessary, for each experiment, the experimental instruments, experimental analysis methods, and experimental conditions (including humidity, temperature, ink, paper, etc.) should be the same for comparison.
Here are some experimental methods I recommend.
1. The Sutherland Rub detector uses the Sutherland Rub detector to make a specific number of reciprocating motions of a printed sample under constant weight to observe the extent of wear on the surface. Because of this method, there is no set value for wear as a standard for anti-wear performance, so some printed samples are required for reference.
2. Anti-tack resistance In some cases, if the cartons are not placed tightly in the box, then during printing, the printed materials rub against each other to generate heat and the carton surface will wear out; the prints will be worn under hot and humid conditions. It will also be reduced because of the hydrophilic nature of waterborne coatings; wear and back-adhesion of printed products can also occur under high-heat conditions. The anti-sticking test results will provide manufacturers with the basis for judging the anti-stick properties. At temperature. In the humidity control room, two printing surfaces are placed opposite to each other to print at a pressure of 500 g/cm2. Leave the temperature at 55°C for 24 hours. This kind of experimental analysis is very reliable and can provide a basis for whether stickiness will occur in transportation. A few printing plants have this kind of experimental device that can perform the sticking experiment. If you do not have such an experimental device, please have a good reputation supplier conduct experiments for your printed matter. It should be emphasized that the experimental results cannot be determined by only one experiment. Instead, a series of samples should be taken for the experiment and the final comprehensive value should be taken.
3. Vibration experiment This is a simulation experiment during the actual transportation process. The experimental results can be used to determine the appropriate packaging material for the customer. Simulated experiments usually take 4 to 6 hours of vibration. This is a very demanding experiment. The experimental analysis is also costly and time consuming. However, in order to minimize customer's dissatisfaction with grinding performance, the loss is minimized. The experiment is still worth it.
One of our recommendations for evaluating the antiwear properties of one of the coating performance indicators is to perform the coating after curing for 24 hours. Although most technicians want to immediately know the experimental results, the coating dry film usually takes 24 hours to cure to the maximum. Excellent performance. Analysis of experimental results should be performed with reference to a sample under appropriate experimental conditions.
How to ensure that the water-based coating oil protects the printed matter without causing problems due to the fact that the ink is not dry due to the undercoating is a common problem. To answer this question, first of all, we should comprehensively analyze the purpose of applying Varnish. It is necessary to have a relatively dry coating layer on the wet ink layer. Ideally, a dry film is obtained to allow the subsequent operation of the wet ink layer, such as die cutting. Waterborne varnish does not accelerate ink drying, and wet ink is still dried through the oxidized conjunctiva. Solvent inks typically take 24 hours to achieve optimal film performance. One of the most critical issues is to ensure the air permeability of the waterborne varnish so that the wet ink layer can contact the air to dry the oxidized conjunctiva.
The second problem is how the printer knows that the printed matter will not be contaminated by the ink in the stack after the online coating. If you expect to immediately rub the printed paper after printing to detect its drying performance, it will be a wrong way. Here are a few suggestions that printers can add to test items:
(1) The glazing technician uses the thumb to press the dark tone area of ​​the printed matter on the printing production line. If the fingerprint disappears after 15-20 seconds, it indicates that the drying performance is good, and the ink will not be contaminated during the stacking process. It needs to be mentioned here that sometimes the printing technician takes the paper out of the stack of printed prints during the printing process, and normally the printed paper should be placed on the observation table.
(2) When coating on the first line, it is necessary to check the condition of the entire stack of paper after printing for 30 minutes, and to inspect the condition of ink smear from the upper layer to the lower layer of the stacked printed sheets. During re-stacking, care must be taken when touching the four corners of printed products that have been coated with varnish to avoid damage.
(3) When spots appear on the coating surface, check whether there is excessive accumulation of coating oil on the edge of the spot area. Too much coating oil will cause the printing product to stick together. There are several ways to avoid glazing; by accumulating, I suggest diluting varnishes with 1% to 2% water (by weight) to reduce their viscosity, or from other points of view, to avoid spotting.
(4) In the UV curing drying mode, the waterborne varnish can be applied with the UV curing ink on-line. When printing with UV inks, as long as the ink is properly cured, better antiwear properties and drying properties are obtained.