In the process of solvent-free mixing, there are very strict requirements for tension control, mainly because of the low initial adhesive force of solvent-free composites, the operation control is difficult, and it is easy for quality problems to occur. In the solvent-free composite process, the shrinkage of the two substrates after bonding is required to be as uniform as possible, otherwise there will be a “tunnel” phenomenon, so in the solvent-free composite process the tension control is more accurate, which is the operation. Personnel put forward a number of requirements, not only to the solvent-free composite tension detection method has a deep understanding and mastery, but also to have the ability to stabilize the control of tension.

First, the application of tension control system and the choice of winding tension mode 
The tension of single-station solvent-free laminating machine is generally divided into four parts, namely, the first rewinding tension,, the second rewinding tension,, channel tension and winding tension. In the process of changing the coil diameter and production speed, solvent-free laminating tension has a constant tension requirement, which plays an extremely important role in improving the winding quality on the basis of ensuring the laminating quality. 
Single station solventless laminating equipment is critical to ensure stable tension and winding integrity due to frequent startup, shutdown, acceleration, deceleration and other operations. 
Floating rollers have the ability to absorb kinetic energy. In the first unwind tension, with constant tension requirements, the second unwind tension, channel tension control uses a cylinder (low friction cylinder) to control the pendulum tension control form, which ensures solvent free. The tension of the laminating equipment is stabilized during acceleration and deceleration, and film stretching and relaxation caused by tension fluctuations are minimized. If the first unwind tension, the second unwind tension, and the channel tension are controlled by a bearing tension sensor, the first unwind unit harness, the second unwind unit harness, the coating harness, and the laminating harness speeds are fully synchronized in order to ensure stable acceleration and deceleration during tension. 
In addition, the flexibility of the guide roll rotation is an important factor to ensure the stability of tension during acceleration and deceleration of the solvent-free laminating equipment. Under normal conditions, the rotation of the guide rollers is synchronized only with the movement of the film, so that the ink on the surface of the film is not scratched. This requires that the static friction between the film and the guide roller surface is greater than the resistance of the roller. Therefore, the guide rollers must be flexible and have a choice of weight. , low-friction bearings, guide rollers, and high assembly precision. The method to determine whether the guide roller is soft is to gently move the guide roller by hand and observe the time required for the rotation to stop, which is generally required to be not less than 15 seconds. Solvent-free laminating equipment rewinding tension and channel tension is a constant tension requirements, winding tension control system mainly includes winding tension, the winding method and taper. Among them, there are three types of winding methods: linear winding, hyperbolic winding and parabolic winding. 
Solvent-free adhesives are characterized by 100% solids content, low viscosity and low initial bonding force. If the laminated inner film is a stretchable film (e.g., PE film or CPP film), try using the hyperbolic winding method. When rolled up, the inner winding volume is relatively loose when collecting a large volume, and the composite film is not wrinkled; the surface of the winding diameter is tightly wound and there are no air bubbles on the surface. 
In addition, the winding pressure can also play a role in assisting the winding, and the air between the film is discharged (some of them have the effect of eliminating static electricity), which can increase the tightness and uniformity of the winding.

Second, retraction tension control mechanism design 
Early solvent-free laminating equipment used cone-top retractable coils. Despite the convenience of charging and unloading, there are disadvantages to the concentricity of the coil, which is directly related to the straightness of the end face, of the paper core. Paper cores used by flexible packaging companies should be reused repeatedly and need to be cut to length. It is difficult to ensure the flatness of the paper core end face and the concentricity of the core. When unfolding, the use of this paper core must have tension interference. When tension is tight, the actual tension fluctuations are more pronounced when bearing tension sensors are used for unwinding. This is one of the main reasons why the unwind mechanism of solvent-free laminating equipment uses a cylinder-controlled pendulum tension control method. 
If the pneumatic cone top shrinkage and unwinding method is used, when the end face of the paper core is not uniform, the core is large and small, the unwinding tension will occur, and if the core is natural, the concentricity cannot be guaranteed. Unwinding after winding; after loading the reel, deformation (different hearts), rewinding and unwinding tension cannot be guaranteed. Also, the applied taper top force damages the flatness of the core end face and makes it difficult to ensure concentricity of winding and rewinding when the core is reused. If the web surface is not concentric during winding, the winding roll will jump up and down. There is no winding pressure on the surface of the wound film during the jumping up of the winding roll, and when the winding roll slides downward, the surface of the wound film will be under high and intense pressure. The winding roll will vibrate periodically, which will cause the wound composite film to wrinkle easily (transverse wrinkles), resulting in a large number of defective products after curing. 
Therefore, an aerated shaft shrinkage and unwinding method should be used, which on the one hand avoids the effect of irregularities in the end face of the paper core on the concentricity of the winding; on the other hand, the slightly deformed core can be rounded, thus maximizing the concentricity of the winding. This is also essential for improving the quality of the laminated film.