Analysis of common problems in laminating compound process

The laminating process is to apply adhesive to the surface of the paper-based printed product and the plastic film, and to bond them together after thermal compression to form a printed product combining paper and plastic. A thin and transparent plastic film makes the surface smoother, which improves the flatness and stiffness of the printed matter, and the coated printed matter has the functions of moisture resistance, waterproofing, stain resistance, wear resistance, and chemical corrosion resistance.

The plastic film composite process finished printed products mainly include various kinds of box packaging such as covers, calendars, food boxes, cigarette boxes, wine boxes, toy boxes and other covers for various books and advertisement albums. According to the different conditions of paper and ink, operators who are engaged in paper-plastic coating are required to make the adhesive and the paper and plastic film firmly adhere to the whole of paper and plastic through appropriate temperature and pressure.

(1) Quality standards of film-coated products:

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

2. The film is firmly bonded, the surface is clean and smooth, no blur, good finish, no wrinkles, no foam, no paper-plastic separation, no trace of powder foil;

3. The size of the slit after the coating is accurate, the edge is smooth, the area of ​​the laminating film is complete, and there is no obvious curl and scratch;

4. The degree of drying after coating is appropriate, and there is no phenomenon of sticking the surface film or paper.

(2) Analysis of common failures of laminating

1. Paper-plastic adhesion 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., the plastic film will be detached from the adhesive layer on the printed matter with a light touch, and the adhesive layer is basically retained The paper surface and the ink layer surface cannot be well bonded to the paper fiber or ink printing layer, and the paper film separation phenomenon is prone to occur on the indentations of book covers, spines and beaks; white cardboard, white cardboard and other packaging boxes During the die cutting and indentation process after film coating, due to the pressure, the paper and plastic appear to peel off.

main reason:

â‘  The paper plant fiber and the plastic non-polar polymer (BOPP) film are two materials with completely different properties. They rely on chemical adhesives to bond them into a solid body. The firmness of paper-plastic bonding depends on the adhesive, so that the two completely different materials, paper and plastic, can be combined into a solid whole. As an intermediate medium, the adhesive must have good affinity for the plastic film, paper, and ink layer at the same time, and have sufficient adhesion. The cohesive force of the adhesive depends on the chemical composition of the adhesive, the nature and proportion of the host material and auxiliary materials, and the synthesis.

â‘¡ The concentration of paper-plastic composite adhesive ratio is the key to determine the bonding force. The essence of paper-plastic compounding is to use an adhesive as an intermediate medium, and to heat and press the BOPP film, printed matter, and ink layer bidirectionally under the action of heat and pressure on the roller of the laminating machine, penetrate, and dry the oxidized conjunctiva, thereby Produce effective adsorption force to make paper and plastic firmly adhere.

â‘¢ There are many factors that affect the poor adhesion of paper and plastic. Various properties of plastic film, paper smoothness, uniformity, paper moisture content, thickness of printed ink layer, amount of auxiliary materials, temperature and pressure during paper-plastic compounding, sanitary conditions of production environment, temperature, relative humidity, etc. Have a certain impact on paper-plastic composite.

2. Foaming

The products that mainly show the film are in the process of slitting, indentation, storage, cover, pasting, die-cutting, etc., in the dark tone position of the four-color overprint, the solid area and the thick layer of the ink, there are sand grains, stripes, worms The paper and plastic in the shape of a tortoise are partially detached.

main reason:

â‘  The coating of the adhesive is uneven, and the adhesion is poor; there are dust and sand particles on the printed film, the environmental sanitation conditions are poor, and the large water content of the paper causes the local paper-plastic adhesion is not strong.

â‘¡There are many times of overprinting on the solid plate, the affinity between the adhesive and the ink layer is poor when the film is coated, the ink color is too thick, and it is easy to form a local separation of the plastic film and the ink layer and cause a "foaming" phenomenon. In order to improve the color saturation in the printing process, various auxiliary materials such as desiccant, diluent, and debonding agent are often added to the ink. Such materials are likely to cause crystallization on the surface of the ink layer, and the surface of the ink layer is smooth and Tough, the adhesive cannot be wetted with it, which affects the paper-plastic adhesion fastness. In addition, when the cover is covered, die-cutting, indentation and other processes after lamination, the air will cause blistering if it is not removed.

â‘¢When the paper and BOPP plastic film pass through the heat pressing machine, the temperature and pressure have a great influence on the adhesion fastness. Paper-plastic two materials rely on the intermediary effect of adhesives, and only under the effect of hot pressing can compound.

Under the action of the external force of hot pressing, the movement of the adhesive molecules is accelerated, and the energy is increased, which is absorbed, diffused, and penetrated by the paper and ink layer of the printed matter and produces a good affinity. The thermosetting property of the binder polymer resin generates cohesion, which makes the plastic film form a strong bond with the printed paper. Appropriate compound temperature, pressure and time are the guarantee for the quality of paper-plastic film products.

â‘£The adhesive is coated too thick, too thin, uneven hot air in the drying tunnel, insufficient temperature in the drying tunnel, uneven adhesive concentration, etc., which causes blistering of the composite product. In addition, the temperature resistance of the adhesive is poor , The acidic effect of the adhesive can also cause blistering.

3. Wrinkle phenomenon during laminating

â‘  The plastic film is wrinkled. The main reason is that the film tension caused by improper traction force in the film during the transportation process is large or small, causing the film to wrinkle diagonally, longitudinally, and transversely.

â‘¡The paper is wrinkled. The main reason is that the paper does not receive heat and pressure flatly and naturally when passing through the heat press machine, and longitudinal or diagonal wrinkles appear, most of which appear in the trailing part. There are also problems with uneven paper and uneven or excessive moisture content.

â‘¢ Paper and film are wrinkled together. The plastic film and paper after the heat-pressing machine appear wrinkled in the longitudinal direction of the trailing part, or the center outward.

4. The finished film is curled

Main performance: When the paper-plastic composite product is cut, it will curl in the direction of the film and cannot be kept flat. In severe cases, it will automatically curl into a cylindrical shape.

main reason:

â‘  The coated paper is too thin;

â‘¡The paper has large water content and high humidity;

â‘¢The temperature in the operation workshop is low;

â‘£ Loose paper and poor flatness;

⑤ The pressure is too high, the temperature is high, and the time is long when laminating.

5. The edge of the film is rough, the film is out, and the hole is broken

Paper-plastic composite products require that the plastic film is completely and completely covered on the paper printed matter, and the edges are smooth, without cracks, and no film. The main reason: there is a problem with the quality of the film, unevenness, and unevenness of the paper when the composite film is conveyed by the rough film. Adjust the side stop plate during operation to make the paper and film convey neatly.

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