When it comes to glue or adhesive, the first thing that everyone thinks of is the glue that is contained in the small bottle. When it is used, it can be applied to the object to be bonded. However, some adhesives are separately contained in two containers, and the two parts must be mixed evenly before use, otherwise, they will not work. Such an adhesive is commonly known as AB glue.
AB glue is much more complicated in form than ordinary adhesives, and it is more troublesome to use. So why do we develop this type of adhesive, what are they unique?
We know that polymer materials are generally obtained by polymerization of many small molecules. For example, a polymer such as polyurethane is often used as a binder. It is composed of two small-molecule compounds. The reaction of a diol with a diisocyanate.
Many glycols and diisocyanates are liquid at room temperature, but the polyurethane obtained after the reaction is a very strong solid. It is not difficult to see that if the compound which is originally in a liquid state can be polymerized to form a polymer after being applied to the surface of the object to be bonded, then no solvent evaporation is required, and we can also cure the glue. Obviously, in this curing process, the molecules originally present in the glue are all left into the polymer without leaving the air, and the environmental and health problems caused by the volatile organic compounds are naturally solved.
But there is a problem that comes with it: how does this adhesive be produced and stored? The diol and diisocyanate react very easily with each other. If they are placed directly in a bottle, and the product is delivered to the customer, the liquid in the bottle has long become a hard solid and cannot be used.
Of course, we can choose some reactants that are not as reactive. At room temperature, even if they are mixed together, they can “peacefully coexist” for a long time. Only when the temperature rises to a certain extent will they polymerize with each other. reaction. This is a way to solve the problem, and in fact, many adhesives do. However, this means that users often need to purchase additional heating equipment such as ovens and hair dryers, and many materials to be bonded cannot withstand high temperatures. At high temperatures, although the adhesive cures smoothly, the object itself is finished. Not the result we want. Therefore, this method has certain limitations.
Another option is to store the two reactants in separate containers, and they have no chance to meet before use, and naturally, they can remain stable for a long time. When it is necessary to bond objects, we only need to mix them and apply them to the surface of the object. Without heating, the adhesive can be cured quickly, so that the two objects can be firmly connected. This is why many adhesives are made in the form of AB glue. In addition to polyurethane, there are many different polymerization reactions that can be used for the curing of AB glue. For example, epoxy glue is another common AB glue.
However, AB glue can be cured without heating, but there are other inconveniences in use. First, the ratio of the two components must be appropriate. For example, in the polyurethane mentioned above, under the ideal reaction conditions, the number of molecules of the diol and the diisocyanate must be one to one. Under these conditions, each diol molecule can react with two diisocyanate molecules simultaneously, and two diisocyanate molecules can also react with two diol molecules at the same time. As a result, two molecules are continuously pulled up. Hand, it becomes a polyurethane with a huge molecular weight.
On the contrary, if the ratio of the two molecules becomes two to one, for example, the number of molecules of the diol is large, when the two meet, the diisocyanate is quickly consumed, and the reaction cannot produce a polymer compound. It can get some small molecules without any intensity. Such a reaction product has almost no mechanical strength and cannot bond two objects together. Therefore, when using AB glue, it is very important to accurately weigh the two components in proportion. Usually, the manufacturer will indicate on the product packaging or in the specification what proportion of the two components need to be mixed.
But weighing the two components in proportion is only half the success. We must also mix the two components evenly so that they can react fully. If the two components are not well mixed, the curing does not proceed smoothly, and the cured adhesive does not have good strength.
Many times, users of AB glue have no conditions to accurately weigh two components, and it is difficult to ensure adequate mixing of the two components. Therefore, in order to ensure the use of AB glue and to provide convenience to users, manufacturers often use special packaging and sizing equipment. A common method is to store the two components in two cylinders that are joined together on the side. When in use, place the cartridges in a manual, electric or pneumatic glue gun, and then make a special nozzle. Connected to the opening of the barrel, as the user operates the glue gun, the two components are simultaneously extruded from the barrel at a certain ratio and mixed evenly in the nozzle. This allows the ratio between the two components to be appropriate and allows them to be thoroughly mixed to ensure the strength of the cured rubber. For larger plants, we can also usefully automated equipment to mix and apply AB glue.