Avoid the defects of the coating process

That is, there are conflicting problems in the adhesive coating process itself such as adhesives and thinners, coating methods and coating uniformity, adhesive amount and adhesive force, drying degree and after-effect. In paper-plastic composites, adhesives are used to create two-way forces on films and paper prints. Effective adhesives must be dried and cured to produce sufficient two-way adhesive strength. That is, the adhesive in the adhesive coating process can be used in the paper-plastic composite production after being diluted and synthesized and diluted. Because of the existence of the diluent, the adhesive cannot form a true dry cure, which is an inherent one. Sexual defects are also the key to easy foaming and release of paper plastic composite products.
The adhesive bond depends on its composition. Adhesives in the main body material synthetic resin, auxiliary material curing agent, plasticizers, etc., need to rely on solvent dissolved before they can participate in the polymerization reaction. Solvent In addition to synthetic adhesives, the main role of the adhesive coating process lies in reducing the viscosity and surface tension of the adhesive, increasing the wettability of the plastic film, and improving the rheology of the adhesive itself.
After the solvent has changed these properties of the adhesive, the adhesive is easy to apply on the plastic film. The content of solvent in all types of adhesives is above 65%. That is, only 1/3 of the binding material is used for adhesives. When paper-plastic composites are used, it is necessary to add 1 more. /4 ~ 1/2 times the solvent dilution, in order to facilitate the coating operation in the actual production. Otherwise, the adhesive does not form a uniform continuous coating on the low surface energy plastic film.
High-dose solvents, which reduce the viscosity and surface tension of the adhesive to facilitate uniform coating on the plastic film, also swell the plastic film and decompose the oil and color in the ink layer, resulting in the adhesive Plastic film, paper and ink prints have a serious reduction in affinity.
Although all types of glue-type laminating machines are designed with hot air drying devices, they are dissolved with various types of resins and chemical raw materials to form solvents in the binder mixture, relative density, boiling point, and specific evaporation rate. The flash point and other properties have undergone major changes and are much more volatile than pure solvents. The pure solvent (toluene) and the binder synthesized and diluted with toluene were uniformly coated on the 20 μm corona-treated biaxially stretched BOPP film surface. After the same hot air bake, the residual toluene solvent was measured. The amount is 21PPm, and the toluene residual solvent mixed in the adhesive is 322PPm, which is a difference of 15.33 times.
This set of data shows that the volatilization rate of the solvent mixed in the adhesive is only 1/15 of the pure solvent. Through the long heating tunnel of the laminator, the feel of the adhesive coating on the film surface was not sticky. This is just the surface condition of the adhesive coating. Generally, the adhesive layer is more than 5 μm, and the solvent in the adhesive coating of 2 to 3 μm under the surface layer is difficult to be used in such a short time (through heating the drying tunnel), so high temperature (40°C to 70°C) °C), the strong airflow (0.4m3/s) is exhausted and the total solvent is included. The surface of the adhesive coating is formed as a "dry-up" and the inside of the outer layer does not dry out.
The solvent of the binder encapsulated in the "dry" skin must gradually evaporate. In the process of gradual volatilization of the solvent, on the one hand, the attached material, the plastic film, does not swell, while the surface of the already dried adhesive layer is infiltrated and softened. As a result of the gradual volatilization, the adhesion and anchoring property to the printing layer of the ink and the paper are reduced, and the formation of a tackiness and blistering is caused, and the film is severely removed.
The use of the adhesive coating process in the production of paper and plastic composite manufacturers, but also pay attention to the direction of the coating roller and the film running in the opposite direction of the coating tend to occur due to the host speed (thrust film operation) and the roller speed does not match (usually the ratio of the two is between 1:1 and 1:2), it will cause the regular coating overlap (coating roller speed is faster than the host rotation speed) or coating dilution (coating roller speed is slower than the host rotation speed), The seemingly uniform motion of the film is due to changes in the rhythm and the contact surface of the rags on the squeegee that changes in rotation speed. The thickness of the adhesive coating is irregular, the degree of drying is uneven, and the adhesion strength appears on the same plane. error.
At the same time, attention should be paid to prints of different printing colors, and the requirements for adhesive concentration and coating thickness are different. The concentration and thickness must be set to ensure that all types of prints meet the adhesive dry basis requirements: see table

Paper type Ink binder amount (dry basis g/m2)
Single 5
Double 6
Offset paper three 6.5
Four 7
Field 8

Single 44.3
Double 4.6
Coated Paper III 5.5
Four 6
Field

Single 6
Double 6.5
Whiteboard paper three 7.5
Four 8.5
Field 9