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We know that the paper-plastic coating will be the comprehensive result of the physical function of thermocompression bonding. Temperature, pressure and speed are the three basic factors to realize this physical comprehensive effect. Correctly handling the relationship between these three is the key to the process operation technology.
Temperature: It is the first key to coating. The adhesive used for pre-coating is hot melt adhesive. Temperature determines the melting state of hot melt adhesive, determines the leveling performance of hot melt adhesive, and determines the molecular orientation of hot melt adhesive. The diffusion ability of three substances, such as BOPP film, printing ink layer, paper substrate, etc., also determines the crystallinity of the hot melt adhesive. Only by correctly controlling the temperature of the working area can the solid heat of the pre-coated film on the film be made The melted adhesive layer melts completely into a viscous flow state, with suitable fluidity to achieve wetting and bonding to the surface of the printed matter, while ensuring immediate solidification after compounding. Make the laminating product flat, bright enough, the adhesive layer melts well, without creases. And can peel off the ink. The temperature control of the coating process also affects and determines the hot-melt adhesive used for the coating to solve the changes when heated, and the resistance to the new heat. Therefore, strict temperature control is the primary key to pre-coating. According to our practice. It is more suitable to control the temperature in the range of 80 ～ 100 C.
Pressure: Appropriate pressure should be used while correctly controlling the lamination temperature, because the surface of the paper itself is not very smooth, only under the pressure, the hot melt adhesive in the state of viscous flow will drive away the air on the surface of the printed matter. Fully wet the paper print surface. Produce colloid molecules to the ink layer of paper printed matter, paper molecules, dislocation, and achieve good adhesion, forming a complete coverage of the entire surface of the printed matter, so that the printed matter is bright, no fog, leveling of the glue layer, no creases , The bonding effect is good. Under the condition of no wrinkle, the pressure should be increased properly to make the thermoplastic curing function of the hot melt adhesive fully displayed. In order to ensure that the laminating products are added after compounding. It has strong resistance to various physical peeling and impact forces. (Such as indentation, hot stamping, hot melt adhesives, etc.) to achieve the perfect uniform speed of the internal structure and surface state of the composite print: the paper film is a dynamic compound motion. The movement speed determines the time that the paper-plastic composite stays on the hot-pressed working interface of the hot-pressed body, and also determines the temperature and pressure input by the laminating machine and the paper-plastic complex cooperation in the actual production process. Actual value. When the film temperature and pressure are fixed.
The change in speed will change the effect of the coating, and due to the upper temperature limit and the pressure supply limit, it will only change from the direction less than the set value, and with the speed increase, the decrease will be obvious, and the hot pressure force will decline. Make the composite effect worse. Running speed is too fast. The bond is not strong. There will be fog, but too slow to be inefficient. Even bubbles.
So the compound running speed. Decided the time for the pre-coated film and paper print to achieve bonding. According to our experience, the general speed control is more suitable for about 10-20 sheets of paper in one minute. (The speed of the electronic laminating machine is smaller due to the hot pressing roller. The speed should be slower)
The actual action value of the three factors of temperature, pressure and speed has a certain range. Due to different equipment. This requires us to find the best effect value in practice to ensure the composite effect of the pre-coating film and create favorable conditions for the spine of the cover of the next step of the adhesive nail cover not to leave the shell and not foam.
The compounding of the pre-coating film and how to create favorable conditions for the following processes (including indentation, bronzing, and wireless binding on the cover, etc.) are also one of the important factors that we should consider in the process of using the pre-coating film for the laminating operation.
When the pre-coated film is combined with the paper print. The lower limit is 80C and the upper limit is 100C. Intuitively based on the high brightness, no fogging, good flatness and no blistering after the composite body is detached from the hot-pressing roller, in this temperature range, the hot melt adhesive can fully receive the heat from the outside to the deep inside Function, the modification of various raw materials in the colloid can be fully exerted, and the entire adhesive layer is completely melted. It produces a true and firm bond, rather than a superficial, shallow layer, which can not be bent or reheated.
When the lower limit temperature is slightly downward, the brightness of the composite product will decrease. When the upper limit temperature rises slightly, bubbles that are not smooth and have different shapes will be scalded on the surface of the film. (This phenomenon is particularly obvious in the electronic laminating machine) Just grasp the critical working area of ​​the laminating temperature. Not only the composite effect is good, but also the hot melt colloid is close to the hot spot of the cross-linking reaction. The curing of the colloid is almost hard, so that it will not be easily softened when it is heated again. This film temperature is very close to the cross-linking reaction temperature.
Recently, when we used a pre-coated film to cover the cover and then bound it for wireless binding, it was found that most of the binding and binding skins that were divided after rewinding had spine detachment and blistering, which made the cover After the film leaves the heat source, the method of water cooling and instant automatic division do not have this phenomenon. (Our equipment is equipped with water cooling system, automatic segmentation system and winding system for selection.) The curing time of the hot melt adhesive for laminating is about 10-15s. The time required for natural cooling at normal temperature in the production environment is greater than this Standard time, especially if the semi-finished product is stacked and wound before splitting. The temperature accumulation between each other is difficult to disperse, allowing natural cooling and solidification
Prolonged, usually naturally slow down and solidify. The hot melt adhesive will gradually generate crystals. The formation of crystals improves the sensitivity of the colloid to temperature, may cause the hot melt adhesive to soften again, and weakens the high temperature coating operation to make it approximate the heat resistance function of the cross-linking reaction, so we use water cooling and immediate automatic Split to prevent heat accumulation, and to create a low temperature quenching and curing zone for the coated products immediately after being separated from the heat source. Let it cool down quickly. The viscosity of the hot melt adhesive in the molten state increases rapidly. Links are too late to move. It is difficult to form crystals, which can make the film-coated product not melt and soften obviously when it is heated again. Perform wireless binding to ensure that the spine does not leave the shell and blisters when the temperature is 30 ° again. In order to ensure the suitability of wireless perfect binding, it has created good conditions and made the quality of perfect binding and laminating products more guaranteed.
In recent years, the coating of teaching materials is basically using pre-coating film. Since we haven't used it for a long time and there are many problems, according to our process practice, it is mainly temperature and pressure that affect the quality of the pre-coating film. The three factors of speed, so correctly handling the relationship between the three is critical to ensure the quality of the pre-coating film and the impact on the production of the next process.