Analysis of Common Problems in Plastic Film Compounding Process

The laminating process is a process of bonding a paper printing product and a surface-coated adhesive plastic film together by heat-pressing to form a paper-plastic printing product. After the film is covered, the printed product has a thin and transparent plastic film on its surface, and the surface is smoother, thereby improving the flatness and stiffness of the printed crystal, and the film-coated printing product has moisture-proof, waterproof and anti-staining properties. Wear resistance, chemical resistance and other properties.

Plastic film composite processing of fine print, there are a variety of books and advertisements album cover, calendars, food boxes, cigarette boxes, wine boxes, toy boxes and other box-type packaging. Requires that the paper-plastic laminating operator select the proper temperature and pressure according to the nature of the paper and the ink, so that the adhesive can firmly bond the paper and the plastic film into a paper-plastic integrated one.

1 Quality standard of film products:

1) According to the different pressures of paper and ink properties, the adhesive should be appropriate; the temperature of the film,

2) Coated film is firmly bonded, the surface is clean and flat, no blur, good finish, no wrinkle, no blistering, paper-plastic separation, no traces of powder and foil;

3) The size of the film after cutting is accurate, the edge is smooth, the area of ​​the film is complete, there is no obvious curling and scratches;

4) Appropriate degree of dryness after coating, no sticking to surface film or paper.

2 coating fault analysis

2.1 paper and plastic bonding is not strong

Main performance: In the post-printing process such as upper cover, indentation, secondary surface processing such as UV film, cutting finished products, etc., a slight touch of plastic film is detached from the adhesive layer on the print, and the adhesive layer is basically retained On the surface of the paper and ink layers, it is not well adhered to the paper fibers or the ink print layer, and the paper film separation phenomenon is likely to occur at the inscriptions such as the cover of the book, the spine, and the koukou; the white paperboard, the white paperboard, and other packaging boxes After die-covering, during die-cutting and indentation processing, due to the pressure, the paper plastic film will appear to be peeled off.

Main reasons: 1 The plant fiber of paper and the non-polar plastic polymer (BOPP) film are two kinds of materials with completely different properties. They rely on chemical adhesives to bond them into a solid one. The degree of firmness of the paper-plastic bonding depends on the adhesive, which combines the completely different materials of paper and plastic into a firm one. As an intermediate medium, the adhesive must have good affinity to the plastic film, paper, and ink layer, and has sufficient adhesion. The adhesive strength of the adhesive depends on the chemical composition of the adhesive, the nature and amount of the main material and the auxiliary material, and the synthesis conditions.

2 The concentration of paper-plastic compound adhesive is the key to determine the bond strength. The essence of paper-plastic composite is the use of a binder as an intermediate medium. Under the action of the external pressure of heating and pressing on the drum of the laminating machine, the bi-directional wetting, permeation, and oxidative conjunctiva drying of BOPP film and printing crystal and ink layer are performed. So as to produce effective adsorption force, make paper and plastic firmly bonded.

3 There are many factors that affect the poor adhesion of paper and plastic. The properties of the plastic film, the smoothness of the paper, the uniformity, the moisture content of the paper, the thickness of the ink layer, the amount of auxiliary materials, the temperature and pressure of the paper-plastic composite, the hygienic condition of the production environment, and the temperature, relative humidity, etc. It has a certain effect on paper-plastic composites.

2.2 Foaming

The main performance: film products in the cutting, indentation, storage, cover, paste, die-cutting and other processes, in the four-color overprint dark position, field and thick ink layer, appear sand, stripe, The worm-like, moire-like paper and plastic are partially detached.

main reason:

1 The adhesive is unevenly coated with poor adhesion; dust and sand particles are present on the printed crystal film; environmental hygienic conditions are poor, and the water content of the paper is large, resulting in localized paper-plastic bonding.

2 In the field version, the number of overprints was too large, and the adhesive and ink layers had poor affinity during coating, and the ink color was too thick, and it was easy to form a partial separation of the plastic film from the ink layer to cause “bubbling”. In order to improve the color saturation during the printing process, various auxiliary materials such as a desiccant, a diluting agent, and a debonding agent are often added to the ink. Such materials are likely to cause the crystallization of the ink layer surface, and the ink layer surface is smooth and Tough, adhesive can not be wet affinity with it, thus affecting paper-plastic bonding fastness. In addition, when the cover is covered, die cut, indentation, and other operations are performed after the film is coated, air is not removed and it also causes foaming.

3 When paper and BOPP plastic film are passed through a hot press machine, temperature and pressure have a great influence on the adhesive fastness. Paper and plastic materials rely on adhesives to mediate their effects, and they can only be recombined under the effect of heat and pressure.

Under the action of the hot pressing force, the movement of the adhesive molecules is accelerated and the energy is increased. The paper and ink layers of the printed product absorb, diffuse, infiltrate, and produce better affinity. The thermosetting properties of the binder polymer resin produce cohesion, which allows the plastic film to form a firm bond with the printed crystal paper. Appropriate composite temperature, pressure, and time are the guarantees for the quality of paper-plastic coated products.

4 When the film is coated, the adhesive is too thick, too thin, the hot air of the drying tunnel is not uniform, the temperature of the drying tunnel is not enough, the concentration of the adhesive is not uniform, etc., and the composite product is foamed. In addition, the adhesive is resistant to temperature. Poor performance, the acidic effects of the adhesive can also cause foaming.

3, wrinkling when filming

1 Plastic film wrinkle. The main reason is that during the transportation process of the film, the tension of the film caused by improper traction force is large or small, so that the film appears oblique, longitudinal and transverse wrinkles.

2 The paper is wrinkled. The main reason is that when the paper passes through the heat-pressing machine, it does not receive heat and pressure in a flat and natural manner, and longitudinal or oblique wrinkles occur. People often appear at the tip position, and there are also paper unevenness and uneven or excessive moisture content. .

3 Paper and film wrinkle together. After the heat-pressing mechanical plastic film and paper appear longitudinally at the tip portion, or wrinkles on both sides of the center outward.

4, film products appear curled

The main performance: When the paper-plastic compound finished product is slit, it will be curled in the direction of the film, and it will not be able to maintain a flat state. When it is severely punished, it will automatically curl into a cylindrical shape.

main reason:

1 The coated paper is too thin;

7 paper moisture content, humidity;

3 low temperature in the operation workshop;

4 paper loose, poor flatness;

5 When the film is covered, the pressure is too high, the temperature is high, and the time is long.

5, film edge rough, film, break

Paper-plastic composite products require the plastic film to cover the paper print completely and completely, and the edges are smooth, free of cracks, and have no film. The main reason is that there is a problem with the quality of the film, which is irregular and rough; when the film is conveyed by the film, the paper is uneven. When adjusting the side shifter during operation, the paper and film are conveyed neatly.

(Text/Zhang Jinyan)