Incomplete curing of compound adhesives II

At the same time, we must also pay attention to the sealed storage, especially the use of solvent drums to store ethyl esters. Sealed storage of this link depends on the conscious of the operator and is not reliable. Then, what is the amount of water in the air diffused into ethyl acetate? Take the example of Shanghai, where the average summer maximum temperature is 33 degrees and the average humidity is 80%, which means that the moisture content per cubic meter of air is about 25 grams. Sufficient to make about 800 grams of curing agent failure. The Kommen company had done tests in the summer, storing 50 tons of ethyl ester in the tank, pumping 5 tons of the pump every day for about 20 minutes, and then sealed and stored. The water content of ethyl ester changes within ten days as shown in Figure 1.

The water content of ethyl acetate purchased by Gaomeng is less than 300ppm (0.03%), but after ten days, the excellent product has dropped to the first grade, and the ethyl acetate content is higher than 1000ppm. This example reminds you that you want to be able to quantitatively monitor the change in stored ethyl ester water.

As you may know, the curing agents of the two-component polyurethane adhesives provided by various manufacturers are excessive, and the excess part is used for the consumption of water and free alcohol and acid for the curing agent, so the commonly used curing agent ratio can be adapted to B in the end. What is the moisture content of the ester? This is related to the working concentration. The 75% solids of ordinary glue is formulated into 25% working concentration, and the ratio is 20:4:48. For example, an ethyl ester with a water content of 1000 ppm (0.1%) will consume 32 grams of curing agent per kilogram, and a 25% concentration of working fluid will use 48 grams of ethyl ester, which will consume 1.54 kilograms of curing agent (32 grams x 48). With the addition of free alcohol and acid, an excess of one part of the curing agent is sufficient, but it must be ensured that the purchased ethyl ester always has a water content of 1000 ppm.

The 35% concentration ratio is 20:4:27.4. Of course, there is no problem with the ethyl ester of superior products. For example, the first grade product with a water content of 2000 ppm will consume 2.75 kg of ethyl ester for 27.4 kg. Curing agent (32gx2x27.4) is also similar. This is by no means advocating the purchase of first-class products. In fact, it is difficult to guarantee that the water content will not increase. As for whether you want to coat with 25% or 35%, it is not your desire but your coating roller.

The typical sample of “incomplete curing” is shown in Fig. 2. The unwrapped roll film will not be crumpled like that. After the tension is removed, the nylon film will slide between layers due to moisture absorption. After a period of time, the nylon film will develop into the shape of Fig. 2. The initial characteristics of “incomplete curing” are not significantly different from those of composite films that have not yet been fully cured. Incomplete curing is an incomplete cure. The difference is that the composite film that has not yet been fully cured can continue curing to a qualified product and the “incomplete curing” composite film. No matter how long it took to mature, it was "sticky," but the degree of stickiness was not exactly the same. Some peeling and peeling is like a non-stick factory, but the bag is heat-sealed and curled (see Figure 2), resulting in fine wrinkles. This is a lighter “incomplete cure” that must be heated to make it sticky; bags made in winter are good; Only when the weather turned hot did it wrinkle, and it was a lesser degree of "incomplete curing." The lesser degree of curing is not exactly the same waste product, even worse than the severely sticky ones, which at the very least wastes the cost of the bag. The lighter ones have to be boiled and delaminated when they are boiled. If they are not boiled, they will be considered qualified products. I propose to “peel” and go to the maturation room to peel it off. A bit higher temperature can be found to be slightly tacky.

The printing film is PET or NY, and the problem is that the transparent part of the hair is often normal and the part of the ink is wrinkled. This type of film is usually printed with polyurethane ink. Generally, polyurethane adhesives contain hydroxyl groups, while non-retort inks usually do not contain curing agents. When the curing agent in the adhesive is consumed by other factors to a critical state, the consumption of hydroxyl groups in the ink is increased. Causes the ink part to wrinkle or peel poorly. The best solution is to add special ink curing agent to the bottom ink, otherwise it can only increase the amount of curing agent. Speaking of the influence of excessive curing agent on the peel strength, according to the experiment, there is only one extreme value, in other words, the intensity above or below this point shows a decreasing trend. Any solution has advantages and disadvantages and needs repeated weighing.

(Text/Jiang Zhongqiu)

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