Common causes and troubleshooting methods in laminating
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The film is made by uniformly coating a layer of adhesive with polypropylene (PP), polyvinyl chloride (PVC) and other plastic films to achieve adhesion to paper under certain temperature and mechanical pressure. A solid process. During the laminating process, the relationship between temperature, pressure and time of the paper and the plastic film passing through the thermocompression bonding mechanism is handled. The fusing phase controls the thickness of the adhesive, the amount of glue, the temperature of the drying tunnel, the temperature of the hot roll, and the mechanical pressure. Factors such as mechanical speed can avoid problems such as blistering and poor paper-plastic bonding during filming.
The laminating process is to apply the adhesive to the surface of the paper printed matter and the plastic film, and after heat pressing, bond together to form a printed product of paper-plastic composite. The printed product after lamination has one more surface. Thin and transparent plastic film, the surface is smoother and brighter, which improves the gloss and fastness of the printed matter, making the printed ink more vivid. The printed products through the film are moisture-proof, waterproof, anti-stain, abrasion-resistant and chemical-resistant. And so on.
The laminating process requires the production personnel engaged in laminating processing to apply the appropriate processing temperature and pressure according to the different properties of the paper and ink, so that the adhesive firmly bonds the plastic film and the printed paper into a paper-plastic composite. Quality standard of coated products: the surface is clean, flat, not fuzzy, good finish, no wrinkles, no foaming, no paper-plastic separation, no powder marks. The degree of dryness is appropriate and there is no stickiness of the surface film or paper. After slitting, the size of the slit is accurate, the edge is smooth, and no film is formed. No obvious curling, seven bends and eight curls.
The printed matter of the plastic film composite process is generally printed in various kinds of box-type packaging such as an advertisement album, various calendars, book covers, packaged food boxes, and wine boxes. The printed products after the surface of the paper has been subjected to film processing, and then subjected to folding, scraping, pasting, baking, die-cutting, indentation and the like. At the same time, it is also affected by chemical substances such as printing and printing ink thinner, various solvents, moisture and dry oil, corrugated paper paste, etc. The printed matter after lamination is subjected to external forces such as folding, scraping, pressing and die cutting. Impact, subjected to higher temperature baking and sunlight, ultraviolet light, and humid environment. Only when these conditions are met can the coated product be considered a qualified printed product.
1 film adhesive and adhesion fastness
The adhesive is an intermediate substance between the printed matter and the film, and mainly serves as a bonding. The performance of the adhesive is one of the key factors determining the quality of the film under certain conditions.
The adhesive used for the film is divided into two types. One is rubber type; the other is resin type. Printing companies must choose adhesives according to the specific conditions of different papers and printed materials. Generally, a rubber type adhesive may be used for a small printing area on the surface of the paper. On the contrary, a resin type adhesive is preferably used for printing a large surface area of the printed product. This is because most of the printed products use resin-type bright fast drying inks. Therefore, the resin type adhesive and the resin type ink film surface are easily bonded, and accordingly, the adhesion fastness is good, and the resin type adhesive generally uses two or more kinds of components, which is To a certain extent, it increases the difficulty of the operator. For example: the ratio of the two resin components of A and B. Problems such as the life of the adhesive after mixing will directly affect the degree of bonding, but as long as the production process is strictly controlled, it can be solved.
During the laminating process, the adhesive must be firmly bonded to the polypropylene plastic film and firmly bonded to the paper. Therefore, the viscosity value of the adhesive directly affects the bonding strength between the paper and the plastic film. In the actual working process, due to the different printing ink layer area of the product, the method of adding the thinning water can be adopted to continuously adjust the concentration of the adhesive. . The surface area of the printed product is small, the binder concentration can be reduced by about 15%, and the corresponding adhesive image area should be increased. Since the adhesives used in each factory are not produced by the same manufacturer, their performance, ratio, chemical composition and adhesive are different. There is no uniform standard and can only be treated differently according to their specific conditions. .
2 wrinkle phenomenon when filming
1 Paper wrinkle phenomenon: The main reason is that when the paper passes through the thermocompression bonding mechanism, it does not flatten the natural heat and pressure, but appears longitudinal or oblique wrinkles, which appear in the tip of the trailer.
2 Wrinkles of plastic film: The main reason is that the film appears in the process of transportation. The tension of the film may be larger or smaller due to improper traction, and the film may be wrinkled obliquely, longitudinally or laterally.
3 Paper and film wrinkle together: The plastic film and paper that have passed through the thermocompression mechanism will wrinkle outward or both at the tip or the center.
3 film blister causes and solutions
The printed matter passes through the film during the cutting, indentation, storage, wrapping, wrap, and stacking of books. In the dark position of the printed multi-color printing, the thick layer of the ink layer is prone to sand-like streaks, worms, The phenomenon of velvety film bulge emptiness, commonly known as "foaming", occurs in a similarly shaped bubble in the white paper portion of the printed layer without ink.
Strictly controlling the production process is an important part of the laminating process. We know that the entire laminating process can be divided into three stages: pre-treatment, lamination, and slitting. In terms of its importance, it is mainly in the first two stages. The purpose of pretreatment is twofold: one is to dehumidify the moisture in the printed product. Since the printing paper emits a large amount of water vapor under the hot pressure of the heat roller, it collides with the colloid. Resulting in the loss of tackiness of the film adhesive, reducing the bond strength and causing the occurrence of bubble phenomenon; second, further curing of the ink layer of the printed product. There will be a certain amount of solvent in the ink layer if it is not pretreated. After the lamination, the problem could not be found within a certain period of time, and the solvent slowly dissipated over time. The colloid is further dissolved slowly, causing the colloid to lose its viscosity and detach the paper from the plastic film, that is, foaming. In the actual work, experiments have been carried out. One type of printed matter is divided into two groups. One group is pre-coated, the other group is not pre-treated, and then the film is coated under the same conditions. After a period of observation, the results are found. There is no blistering in the treatment, and it is easier to blister without treatment. Therefore, it is necessary to carry out pre-treatment, so that the various solvents in the ink layer are volatilized as soon as possible, so as to ensure the permanent firmness of the adhesion strength.
In the actual work, the cover skin, calendar, card, packaging, etc. after the film was found, and no foaming was found after the process of sealing the bread book, cutting the book, and packing. But after a while. After the delivery, the customer found a bubble. It is confusing, but it is actually not an incomprehensible phenomenon. It is also fully illustrated that the foaming after the filming has a great relationship with the solvent and other chemical components contained in the ink layer, especially the large area of the printed image is more obvious. Pre-treat the product before laminating. There will be no such phenomenon. It is necessary to strictly control the production process. Of course, there are other factors that cause the film product to be weakly combined. For example, the adhesive itself has quality problems, the binder is too thick, too little water is added, the machine speed is too fast, the temperature is too low, and the pressure is small. For reasons such as too much paper dust, as long as the process management is strengthened, the acceptance of raw materials into the warehouse is strengthened. The quality of materials purchased at a fixed point can be solved. In addition, the cover, packaging, advertising, and the like which require the film are placed for a period of time after printing, and the conjunctiva is completely cured in the glue layer in the ink layer. After the solvent has evaporated, the film is coated. It is also possible to overcome the problem of foaming.
4 temperature, pressure, machine speed, the amount of glue on the adhesion fastness
Paper and plastic film are the effects of temperature, pressure and machine speed on the adhesion fastness through the thermocompression mechanism. Two kinds of materials, which are irrelevant, rely on the adhesive to mediate. Recombination can only be achieved under the influence of thermal stress.
Under the action of external pressure of hot pressing. The movement speed of the binder molecules is accelerated.
The ability is increased, and the paper and ink molecules are attracted to the spread. Penetrate into the paper print and ink layer to produce better affinity. Solidification occurs. The cohesive force generated by the thermosetting property of the binder polymer resin forms a firm bond between the plastic film and the printed paper. The appropriate compound temperature, pressure, compounding time, amount of adhesive applied, etc. are the quality of the paper-plastic composite product. Protection.
1 drying tunnel temperature is controlled at 40 ~ 45 ° C;
2 hot rolling temperature is controlled according to the technical specifications of different types of adhesives at 50 ~ 80 ° C;
3The mechanical pressure is proportional to the cohesive force. The pressure is strong and the adhesive force is small. Under the action of strong pressure, the adhesive is more beneficial to penetrate into the paper to improve the adhesion. Therefore, it can withstand mechanical energy. In the case, the pressure is better than the small point, and the surface pressure is controlled from 100kg/cm 2 to 150kg/cm 2 ;
4 The speed of the machine is related to the pressing time, which will determine the length of the pressing time. The length of the pressing time is related to the adhesive force, and the bonding force with a long pressing time is longer than the short time. In general, the speed of paper smoothing can be faster, and the paper is slower than the machine speed;
5 coating adhesive with the amount of glue, based on experience, according to the roughness of the paper, the size of the printed graphic area, different paper to adjust the amount of glue. Paper smoothness is poor, rough or ink layer coating should be larger. Conversely, the amount of coated paper with a high degree of smoothness should be smaller.
5 film finished products appear curled
The main performance is that after the composite product is cut, it presents a curl in the direction of the film and cannot maintain a flat state. When it is severe, it is automatically curled into a cylindrical shape. The main reasons are: 1 the film is too thin; 2 the paper has a lot of water content, high humidity; 3 low temperature; 4 paper loose, flatness is poor; 5 film pressure, high temperature, long time.