Plastic head process improvement

At present, our factory's high-volume teaching aids test series uses plastic head technology to complete the binding work. The binder is mainly polyvinyl acetate, commonly known as white latex. White latex is used to solve the problem of stickiness of offset paper glue heads. Now the supplementary papers use coated paper as the cover, and the cover and the book core are made of white latex as the adhesive to glue the head. After cutting and handing over to the user, the cover and the book's heart are scattered during the process of moving or leafing. We believe that the quality of the white latex is caused by poor quality, and for some brands of white latex, we can't solve the problem. Later, by borrowing from the experience of other factories, the tool was used to draw the hairs at the places where the glue was needed. The pull of the paper pulled the cover from the book's heart. However, it basically did not solve the problem, and the appearance was not beautiful and was easy to hurt. The series of supplementary examination papers are larger in format, generally they are open sixteen or three, and the existing wireless glue binding equipment cannot be used, and users do not allow wire binding. Under large batches of tasks, artificially applying covers is not only time consuming but also not beautiful. After observation, it was found that the traditional plastic head can only form a film on the back surface of the book. If the glue can enter the interior of the paper and form the side glue to achieve the effect of glue binding, then the cover bond is naturally strong. After many experiments, the binder and the process were improved to achieve the desired results.

1 Traditional plastic head technology and principle analysis

The traditional plastic head process flow: with posts - cutting - coated binder - drying - split - cutting.

Principle analysis: The glue used to glue the head when binding is mainly polyvinyl acetate, which is white latex. For offset paper, since the surface of the offset paper is rougher than that of coated paper, the offset paper is more likely to be wetted by the adhesive and the bond should be firm. The coated paper is a paper coated with a white paste on the base paper and then pressed. The smoothness is high, and the binding material is not easy to wet and does not easily penetrate into the interior of the adhered material. Therefore, when bound with coated paper as a cover, the cover and the book core are not adhered by the adhesive, and the adhesive film formed on the back surface of the book is adhered by the adhesive only, and the contact area between the cover and the film is too small. Causes poor adhesion. In addition, the film formed of polyvinyl acetate is completely dry and has poor flexibility, and is prone to brittleness.

2 Improved Process and Principle Analysis

Process flow: with posts - cutting - coated binder 1 - dry - coated binder 2 - dry - split - cutting.

Principle analysis: In the improved process, the choice of binder is critical, and the binder must be able to fully wet the surface of the adhered material. For bonded materials, surfaces with a slightly rougher surface and a smoother surface can have a greater area of ​​contact with the adhesive; for adhesives, the fluidity of the adhesive must be ensured. All surfaces of the surface of the adhered object can be filled. Binder viscosity and concentration must have certain requirements, thick binder in the solid content, less water, cohesion, bonding strength is high, easy to set after drying, but its poor mobility, difficult to be infiltration The surface of the adhesive material does not easily penetrate into the interior of the material, so thick adhesives are used where the adhesive area is small but large adhesive fastness is required. The thinner binder has less solid content and more moisture, so it has good fluidity, and is easy to infiltrate and penetrate into the interior of the material after being coated on the surface of the adhered object, but its cohesive force is small, the viscosity is small, and the adhesion fastness is not strong enough. Therefore, it is suitable for bonding areas with larger areas.

3 Why use a secondary coating adhesive

According to the analysis of the principle of the binder, the thin binder can penetrate into the interior of the adhered object, but the adhesive fastness is not strong enough; and the thick binder has poor fluidity and does not easily penetrate into the adhered object. Therefore, applying a binder is not enough to achieve a firm bond. Therefore, the first time the adhesive is thinned to penetrate the inside of the adherend, but the adhesive strength is not enough. The second thicker adhesive strengthens the adhesive strength.

4 Binder choice

The choice of Binder 1 and Binder 2 is not the same. The purpose of applying the binder 1 is mainly to infiltrate into the side glue to increase the area of ​​the binding between the cover and the book block. The purpose of applying the binder 2 is mainly to form a gum with high adhesive strength.

Binder 1 is a binder made of polyvinyl alcohol as a main raw material and some auxiliary agents. This is because the surface of the coated paper is smooth, and the polyvinyl alcohol film has good film forming property and strong viscosity. After being re-warmed, the polyvinyl alcohol has very good fluidity and can easily penetrate into the adhered object.

Binder 2 is mainly white latex, and some additives that increase its flexibility and bond strength can be added. After the white latex is dried, it is easy to be brittle, which is good for the cost, but it is easy to precipitate when it is diluted too much. It should not be used as the binder 1.

5 problems that should be paid attention to during operation

The bound book is firmly bonded under a certain tension, and the cover and book heart do not spread.

When binder 1 is applied, the book should not be stacked too high. The stacked book is too strong under the pressure of the book, and it is difficult for the binder to be completely absorbed. Generally, the height is 25 cm to 30 cm. It is also not possible to use heavy materials on the top of the book to apply adhesive material. When coating, it should be uniform. It is necessary to ensure that each book can be fully absorbed. Finally, the binding between the cover and the book center is about 1 mm to 2 mm. The next procedure.

After the adhesive material 1 is absorbed, the adhesive material 2 can be applied at this time. At this time, the material is pressed on the upper surface to prevent the adhesive material from infiltrating. The amount of adhesive agent used should be moderate and uniform, and the strength of the adhesive film should be good.

In order to meet the binding requirements, a secondary coating process was used to extend the drying time of the book, which generally takes 2 hours to perform the split work. When the temperature is low, it may be longer. If the adhesive force of the glue is not fully formed yet, the cover is easily separated from the book center. If the drying time is too long, a certain force must be used to separate the book from the book, and it is also easy to separate the cover from the book center.

Adhesive 1 and binder 2 contain water and volatiles. Do not expose it to the air for a long time, which will change the concentration of the ingredients and affect the quality. It is best to use as much as you like.