Third, the use of hot melt adhesive film and adhesive glue hot melt adhesive is not adaptable
The end use of the hot melt adhesive for the film is to complete the paper/plastic composite. The hot melt adhesive transforms from a solid state to a liquid state, and undergoes and recombines in a repeated deformation from a liquid state to a solid state. Thermoplastic cure can only be achieved if it falls to room temperature. That is, "hot reheat solid."
The final purpose of the glue hot melt adhesive is to complete the cover and book block. It is also under the condition of temperature change under heating and cooling that the hot melt adhesive changes from a solid state to a liquid state. Brushing the book back and pasting it with the cover, and then reverting to a solid state, the combination of the cover and the book block can be formed. Is "hot pack cold."
Laminating and binding processes and production operations have common requirements for hot melt adhesives. Without the increase in temperature during processing (to the technically required lower limit temperature), it cannot be produced. Film and glue are not in the same production line. According to the processing sequence, the film is on the front and the glue is on the back. Of course, the cover film of re-cold-solid coating touches the hot-melt adhesive that is applied to the back of the book in the liquid state after heating, and the glue-binding hot-melt adhesive that is still in the heated and melted state will cover the hot-cold coating film. Through the conduction of the cover paper substrate, the temperature is delivered. In order to reach the contact interface (the combination of book back and cover) - the balance between the temperature of the contact body (cover - glue hot melt glue - book block). This heat transfer phenomenon will initiate the warming-softening-tacking change of the cold glue that the cover of the cover film is cured, and the emptying of the book back film will occur. In the same way that hot melt adhesives are used, why does this incompatibility or incompatibility occur?
The use of hot-melt adhesives for laminating film pursues the adaptation to the BOPP plastic film's affinity and thermal shrinkage limiting temperature (120°C). Through the optimization of polymer materials, blending, modification, polymerization into medium-temperature colloids.
The hot melt glue used for glue binding pursues the outstanding fluidity of the deep groove of the milling groove of the book block album. On the one hand, the flow properties need to be adjusted with a variety of modifying materials, and more importantly, it is guaranteed by high temperatures. There is a gap in the use of temperature between the two types of glue. Glue-binding hot-melt adhesives are high-temperature colloids whose melting temperature is higher than that of hot-melt adhesives for film coating.
The cold-fixed film cover, when entering the glue-binding line, touches the high-temperature hot-melt adhesive on the back of the book and on both sides. Around 170 °C high temperature primer and side glue. After about 3 to 10 seconds of operation, it is less than the curing time of 30-50s), higher than the Global Softening Point of 73-78°C), and also higher than the softening point of the hot-melt adhesive used for the film (solvent-free melt coating type Pre-film 85 °C, solvent evaporation coating type quasi-pre-film 60 °C). In the molten visco-elastic state, stick with the cover.
At this moment, the temperature of the hot melt adhesive on the adhesive cover and the booklet album is still higher than the softening point of the precoat hot melt adhesive used on the cover film. At the moment and the beginning of the contact between the two, three new changes will occur:
1. The back of the book is brushed with a 1.0 to 1.2 mm thick glued-adhesive hot melt layer, which conducts cooling to the inner album while also conducting to the cover. And through the cover of the paper, the outer layer of conductive layer to the ink layer - coated with hot-melt coating - BOPP plastic film (see Figure 10).
2. The back of the book is coated with a 1.0 to 1.2 mm thick hot melt adhesive layer, which is measured on the back plane of the book. It does not include hot melt adhesives that are recessed 1.0-1.5mm deep (see Figure 101-1...1-n). As far as the entire book is concerned, due to the presence of regularly spaced milling slots, there is bound to be glue trimming within the same slot. There is also a rule that the amount of brushing is not the same across the entire area of the same book. The amount of glue applied is more or less regular, resulting in slow or rapid heat dissipation after painting. The temperature that causes the glue on the back of the book must be more or less with its amount, and it will reflect a difference of high or low accordingly. That is, the temperature conduction of the glued hot melt adhesive that the film cover receives is not the same as the isothermal one. The thermal conduction of adhesive glue used in the glue has both vertical and horizontal conduction from the cover to the cover and from the near and far to the inner leaflet. At the same time, there is also the high-temperature and low-temperature lateral conduction in the glue layer. This is carried out independently of each other, but they are crossed, mutually influenced, mutually dominant, or merged, or reduced, not according to the complex performance of mathematical calculations.
Figure 10 glued hot melt adhesive temperature transfer schematic
3. Brush the primer and the side glue on the back and both sides of the book. Relatively speaking, the primer brushing amount is large and the brushing time is early; the side brushing brushing is less and the brushing time is late.
The cover is affixed, first contact with the primer, and immediately contact with the side glue. The time of the order of the cover and the cover is poor, which is slightly less than the time difference between the primer and the side brush.
The contact area between the cover and the primer is the full area of the back of the book. The contact area with the side glue is a linear or narrow band shape of 3 to 7 mm. The side glue contact area is smaller than the bottom glue contact area.
These three dynamic changes will result in a higher remaining temperature of the glue-adhesive hot melt adhesive. The reheating of the film-covered hot melt adhesive will make the coated hot-melt adhesive not adaptable to the glue-adhesive hot melt adhesive. Phenomenon:
1. The composite film covering the cover, in the horns on both sides of the back of the book, appears straight or stripped;
2. The back of the book is completely removed from the paper substrate (or ink print).
3. The back of the film was partially removed from the back of the book.
4. At the side of the plastic coating brush or the side of the adhesive pressure line, the thin film in the form of a line or a strip is removed.
Fourth, the adaptability between adapting processes can be solved through the adjustment of materials
The raw material configuration of hot melt adhesives designed for the convenience of process operation has caused the inadequacy of the process convergence. This kind of different kinds of hot-melt adhesives' self-contradictory influence can be completely resolved through the high speed of materials. There are many successful examples in China.
(I) Hot melt adhesive for film
Currently used pre-film hot-melt adhesives have two problems: colloidal composition and coating method.
