Abstract:This article mainly introduces the control points of the solvent-free composite process,including,temperature control,coating amount control ,tension control,pressure control,ink and glue matching,controlling humidity and its environment,glue preheating,etc.
Solvent free composites are increasingly being used, and how to make good use of this process is a topic of concern for everyone. To make good use of solvent-free composites, the author strongly recommends that enterprises with conditions use multiple solvent-free equipment or double glue cylinders, that is, use two glue cylinders, one containing a universal adhesive that covers most of the product structure, and the other selecting a functional adhesive suitable for the surface or inner layer as a supplement based on the customer’s product structure.
The benefits of using a double rubber cylinder are: it can increase the application range of solvent-free composites, reduce emissions, have low costs, and high efficiency. And there is no need to frequently clean the glue cylinder, switch adhesives, and reduce waste. You can also choose adhesives based on product and customer requirements to ensure product quality.
In the process of long-term customer service, I have also summarized some process control points that must be paid attention to in order to do a good job in solvent-free composite.
1.Clean
To achieve good solvent-free composite, the first thing to do is to be clean, which is also a point that is easily overlooked by enterprises.
The fixed rigid roller, measuring rigid roller, coating roller, coating pressure roller, composite rigid roller, mixing guide tube, main and curing agent barrel of the mixing machine, as well as various guide rollers, must be clean and free of foreign objects, because any foreign object in these areas will cause bubbles and white spots on the surface of the composite film.
2.Temperature control
The main ingredient of solvent-free adhesive is NCO, while the curing agent is OH. The density, viscosity, performance of the main and curing agents, as well as factors such as the service life, temperature, curing temperature, and time of the adhesive, can all affect the quality of the composite.
Solvent free polyurethane adhesive has high viscosity at room temperature due to the absence of small solvent molecules, high intermolecular forces, and the formation of hydrogen bonds. Heating up can effectively reduce viscosity, but excessive high temperatures can easily lead to gelation, generating high molecular weight resins, making coating difficult or uneven. Therefore, controlling the coating temperature is very important.
Generally, adhesive suppliers will provide customers with some usage parameters as a reference, and the usage temperature is generally given as a range value.
The higher the temperature before mixing, the lower the viscosity; the higher the temperature after mixing, the higher the viscosity.
The temperature adjustment of the measuring roller and coating roller mainly depends on the viscosity of the adhesive. The higher the viscosity of the adhesive, the higher the temperature of the measuring roller. The temperature of the composite roller can generally be controlled at around 50 ± 5 ° C.
3.Glue amount control
According to the different composite materials, different amounts of glue can be used. As shown in the table, the approximate range of glue amount is given, and the control of glue amount in production is mainly determined by the gap and speed ratio between the measuring roller and the fixed roller.Glue application amount
4.pressure control
Due to the fact that the coating roller controls the amount of glue applied by the gap and speed ratio between two light rollers, the size of the coating pressure will directly affect the amount of glue applied. The higher the pressure, the smaller the amount of glue applied.
5.The compatibility between ink and glue
The compatibility between solvent-free adhesives and inks is generally good nowadays. However, when companies change ink manufacturers or adhesive systems, they still need to conduct compatibility testing.
6.Tension control
Tension control is quite important in solvent-free composite because its initial adhesion is quite low. If the tension of the front and back membranes does not match, there is a possibility that during the maturation process, the shrinkage of the membranes may be different, resulting in the appearance of bubbles and tunnels.
Generally, the second feeding should be reduced as much as possible, and for thicker films, the tension and temperature of the composite roller should be appropriately increased. Try to avoid curling of the composite film as much as possible.
7.Control humidity and its environment
Regularly monitor changes in humidity and adjust the ratio of the main agent and curing agent accordingly. Due to the fast speed of solvent-free composite, if the humidity is too high, the composite film coated with glue will still come into contact with the moisture in the air, consuming some NCO, resulting in phenomena such as glue not drying and poor peeling.
Due to the high speed of the solvent-free laminating machine, the substrate used will generate static electricity, causing the printing film to easily absorb dust and impurities, affecting the appearance quality of the product. Therefore, the production operating environment should be relatively closed, keeping the workshop within the required temperature and humidity range.
8.Glue preheating
Generally, the glue before entering the cylinder needs to be preheated in advance, and the mixed glue can only be applied after being heated to a certain temperature to ensure the transfer rate of the glue.
9.Conclusion
In the current stage where solvent-free composite and dry composite coexist, enterprises need to maximize equipment utilization and profits. The process can be solvent-free composite, and it will never be dry composite. Reasonably and effectively arrange production, and effectively utilize existing equipment. By controlling the process and establishing precise operation manuals, unnecessary production losses can be reduced.
Post time: Dec-21-2023