If water-borne adhesives are used in composite film, how to achieve good composite effect and how to make peeling strength better after composite film maturation.
1. Can water be diluted?
At present, most of the water based adhesives on the market are emulsion type. The principle is that polymer polymers depend on emulsifiers in water. It is actually a sub stable state. Many external forces will lead to latex demulsification and loss of function.
Therefore, it is not recommended to dilute the glue with water. Because water dilution will increase the surface tension of the glue, destroy the stability of the glue and lead to delamination. In addition, dilution will change the surface properties of products, resulting in poor wettability, affecting the composite appearance.
2. Does the water-borne rubber composite film need to be ripened?
Generally speaking, water-borne rubber composite membranes do not need to be ripened, so they can be sliced off the machine. Proper ripening for a period of time can improve peeling strength, because the molecular weight of water-borne adhesive is very high, composite film manufacturers need a certain time to leveling to achieve better strength.
Therefore, when conditions permit, it is better to put the composite film in a 50 C ripening chamber for 1 h to 4 h. The strength of composite membranes is affected by long-time curing at higher temperatures (above 80 C), because water-borne rubber polymers can not withstand long-term high temperatures.
In the process of composite film, there will be a series of problems, such as weak composite, white spot, difficult heat sealing, and so on. The recipe answers these problems one by one, and the relative countermeasures.
I. Insufficient Composition
That is, the composite strength is very low or zero, which can not meet the customer's requirements, resulting in product scrap. Due to the particularity of the composite film production process, low surface tension, high content of smoothing agent, surface pollution and so on may lead to poor composite.
1. Low surface tension
Generally speaking, the surface tension of dry composite film must be above 38dyn/cm before it can be used.
The practice of composite film manufacturers has proved that if the surface tension value of composite film is lower than 38dyn/cm, the composite strength may be low. When the composite strength is lower than 36 dyn/cm, the composite strength will be very low or zero. At the same time, the composite strength is also related to the thickness of the composite film. If the thickness is less than 30 micron, the composite effect can meet the requirement basically when the thickness is 36-38 dyn/cm and the surface tension is 37 dyn/cm, depending on the composite structure, such as OPP/PE. However, when the thickness is greater than 50 microns, it can hardly be used below 38dyn/cm.
The surface tension of the composite film is very high when it is just produced, but it decreases gradually with the increase of storage time. Generally, the composite film can be stored for 3-6 months, but the storage period should not exceed 2 months in the hot and humid summer season. Practice has proved that the surface tension value of the composite film is closely related to the surrounding environment and the thickness of the film. The higher the ambient temperature and humidity, the faster the surface tension value decreases, the thicker the film, the faster the decline. Therefore, the placement of composite membranes should not exceed 3 months, especially in the rainy season. More attention should be paid to the ventilation and ventilation of storage. If the storage time is too long for some reason, in order to avoid loss, besides volume-by-volume inspection, comprehensive consideration should be given to whether to continue to use the composite products according to their use.