The relationship between the index of laminating glue and common problems

I. Viscosity

Viscosity is the internal friction of the liquid, and colloquially, the thin consistency of the glue.

The viscosity of the glue does not indicate the bonding performance of the glue, in other words, the thicker the glue is, the better the performance is. The viscosity can be adjusted within a certain range.

The viscosity will mainly affect the coating leveling of the adhesive, the amount of adhesive and so on.

◎ The influence of viscosity on coating and leveling

Glue viscosity has a very large influence on coating and leveling. Generally speaking, too thick and too thin glue will cause coating difficulties and poor leveling. The appropriate viscosity range is the necessary prerequisite to ensure these two items.

If the viscosity is too thick, the glue is not easy to spread out after coating, and it is easy to appear a line. The glue viscosity is too low, easy to appear flower, in extreme cases will appear flow hanging phenomenon.

◎ The influence of viscosity on the amount of glue

The viscosity of glue also has a great influence on the amount of glue, and the change of the amount of glue has a key role in the compound effect. Normally, the higher the viscosity, the greater the gluing, the lower the viscosity, the smaller the gluing.

It should be noted that, with the change of the speed of the cots, the amount of glue is also changing.

Change of glue amount: h=2/3kμu

h- adhesive thickness     μ- viscosity      u- machine speed          k- constant

As can be seen from the above formula, the greater the machine speed, the greater the viscosity, the greater the amount of glue, the greater the thickness of the adhesive layer.

◎ Method for the determination of viscosity

The commonly used measurement methods of viscosity are outflow cup method and rotary viscometer method. It should be noted that the viscosity measured by these two methods is not the same type, and there is no conversion relationship between them.

Drain cup method

Commonly used is coated with 4 cup method and Chaen cup method, its principle is the same, the determination of the specified volume of liquid, through the specified diameter of the mouth of the time required, this way generally determination of low viscosity liquid, such as coated with 4 cups, for the determination of more than 120 seconds of the liquid is not applicable.

It is important to note that the 4 cups is short for No.4 cup, the Chayn cup also has No.4 cup, do not confuse the application process

Rotary viscometer method

This method is mainly used to measure the liquid with larger viscosity. It is used to measure the resistance of the liquid in the process of liquid rotation.

Common laminating glue is generally 17-30s (coated with 4 cups)

The viscosity of glue used for automata is lower than that of hand motors.

Four, mechanical stability

Polymer emulsions subjected to various forms of mechanical shear will give the latex particles considerable energy, when this energy exceeds the coalescence activation energy, the emulsion will lose stability and flocculation, demulsification. Simply put, mechanical stability is the ability of the glue to resist shearing.

The mechanical stability has a great influence on the gluing effect and the glue production.

■ Influence of mechanical stability on gluing effect

In the process of application, there is friction and shearing of glue at the scraper, and the adhesive with poor mechanical stability will appear more flocculent at the scraper, which makes the coating in the film adhesive layer produce sections of stripes, affecting the coating effect.

■ Influence of mechanical stability on production

The production process of glue is inseparable from stirring and other equipment, which will produce shear force on glue. If the mechanical stability of glue is poor, there will be a large number of caking and even demulsification in the production process.

The determination of mechanical stability: In addition to the method of measuring mechanical stability with instruments, there is a simple way to determine the mechanical stability of glue in the practical application process, that is, the finger twisting and kneading method. The mechanical stability of the glue can be roughly understood by the number of turns without breaking the milk.