Gravure printing plastic film quality control method

Plastic flexible packaging products are generally printed on various plastic films, and then a composite film is formed by combining a barrier layer and a heat seal layer, and the product is cut and bagged. Printing is the first process of production, and it is also the most difficult process to control. Most of the quality problems of products appear in this process. The quality of a packaging product is measured, and the quality of printing is the first. Therefore, understanding and controlling the process and quality of printing becomes the key to flexible packaging production. Gravure printing is the main printing method for today's plastic film printing. The use of gravure printing for plastic film has the advantages of fast speed, rich colors, clear and bright, moderate contrast, vivid image, and various product specifications. The gravure printing has a high printing resistance, and the large-volume prints with more than one million prints have more advantages.

The quality requirements of the gravure plastic film products are relatively high. The quality standards of the printed appearance are as follows: 1 After the flowering process, the color pattern registration error is not more than 0.3mm. 2 check the specifications of the film, the color pattern registration error is not greater than 0.3mm. 3 Check the ink color of the printed product, and it is required that the hue is correct, bright and uniform, the ink is bright, the ink is soft, and the edges are bright and clean. 4 printing fastness, requires transparent tape stick ink does not decolorize. 5 pattern text lines, requiring clear and complete, not incomplete, no deformation. 6 Textures are rich in requirements, and outlets are clear. 7 The product is clean and tidy, with no visible dirt or knife. 8 Requirements of the product with the same color density deviation and the same batch of the same color and other indicators meet the requirements of GB7707-87.

In order to better achieve the above quality requirements, we can control the gravure plastic film process from the following major aspects: 1. Grasp the process points of various plastic packaging film substrates 1 BOPP is the most commonly used printing substrate. The main point of its production process is a typical plastic gravure production process; use polyamide or chlorinated polypropylene ink printing, appropriate tension and imprinting force, and the drying temperature is controlled below 80°C. 2BOPET printing points: Because PET is usually thin, easy to wrinkle, printing requires greater tension, the ink has a certain degree of selectivity, easy to use the general printing ink layer, the film static, prone to block version (not access to the Internet ), fluffing and knife marks (knife wire) phenomenon, printing workshop humidity is good. 3 BOPA printing points: BOPA is a film that is easy to absorb moisture and deform. Therefore, the printing machine must ensure that the environmental humidity of the printing machine cannot be too high (if the dehumidification measures are not sufficient, the humidity is not suitable for the printing of nylon film); the unprinted film cannot destroy the original aluminum film packaging film and must be printed immediately after opening. Nylon film should be preheated during printing (if the machine does not have a preheating device, the plate can be mounted on the second color, leaving the first color as preheating), and the preheating temperature is 50-80°C; The printing tension should be appropriately reduced; the pressure should be moderate; the ink should be adaptable; depending on the choice of product structure, if it is a cooking bag, cooking ink must be selected; after printing, the product must be tightly packed, stored in the dried-recycled room, and stored as soon as possible. complex. 4K coating film (KOP, KPA, KPET) printing point: Because K coating film is roller or spray type, its thickness uniformity is not very good, the surface is uneven, and PVDC is just brittle, when printing The printing tension and the imprinting pressure cannot be too large, the overprinting is difficult, the ink transferability is poor, and when printing a light screen plate, it is easy to get a flower point (parts of the network points are lost), and a higher hardness press roller is used for printing. In addition, the solvent is selective. If the solvent is used improperly, the coating may be dissolved, the residual amount of the printing film solvent is large, and the adhesion is easy. Therefore, special attention must be paid to drying and cooling. The printing of the matte film can be printed on the glossy surface using the OPP process. However, because the matt layer on the surface cannot withstand high temperatures, the drying temperature needs to be controlled. 5 The pearlescent film is printed with a table printing ink, and try to use a good table printing ink. The heat shrinkable film should be printed with a very low drying temperature. Special heat shrinkable ink should be selected (the printed ink layer should be able to shrink without falling). If it is a PVC heat shrinkable film, consider the solvent to dissolve the film. Sex. 6 The tension of unstretched PP and PE films should be small when printing, and it is difficult to overprint. The amount of deformation of the printing should be fully taken into consideration when designing the pattern.

2. Prepress process development 1 plate design. At the time of plate making, the original designed by the design company needs to be modified according to the characteristics of gravure printing, so that it can be more suitable for printing needs. For overprinting needs, such as small lines and texts cannot use multi-color overprinting, the pattern of color registration should not have small anti-white characters, and should not be left blank on the color registration pattern, and other small words should be put on. Yan version, black, blue, red, yellow version as far as possible between the other color version. For printing needs, the bar code should be arranged in such a way that the line direction is consistent with that of the cylinder. In terms of color guarantee, if there are conditions, it is best to separate the plate from the ground and color patterns, and use the special version as much as possible. Hanging screen version must fully consider 80% and 5% of these two color jump areas, and the limit of the screen points when the gradient is suspended is more than 10%. 2 ink deployment. The adjustment of the printing ink adaptability, such as ink viscosity, concentration, the principle is to adjust the viscosity of the ink with a diluent (solvent) adjustment, according to the situation of the printing roller and the machine to determine the ink viscosity before printing, according to the solvent in the printing process Volatile conditions often add solvent, but can not be excessive, try to ensure that the ink viscosity is the same; ink to talk about, you must use diluting agent (dipping oil), avoid using solvents to dilute. Ink color deployment. In this regard, the following points need attention: Observe the color of the light source as much as possible using the standard light source (D65), if there is no standard light source, it is better to have a sunny north direction. When preparing spot colors, primary color inks should be used for deployment. The primary color inks referred to here are the inks directly produced by the ink factory. The brightness and saturation of the ink color can be guaranteed. Color matching is performed with as few ink colors as possible. The more colors, the greater the color matching error and the greater the difficulty of rematching.

3. Proofing When a set of plates is printed, a standard proof must be confirmed. Some manufacturers take the sample draft of the plate making factory as a standard sample, and they cannot be sampled at the time of final delivery. Therefore, the printing machine must be used for proofing before printing, and the customer or the relevant person will confirm it as a standard sample. The printing of the standard sample should be carried out under the normal printing process conditions, otherwise it will be very difficult to trace the sample after printing. Therefore, the following points should be noted when proofing: 1 The process conditions select the most basic printing process conditions. 2 ink viscosity as low as possible. 3 The original color ink should be sampled after adding a certain amount of diluting agent. Use the contaminated ink that has been used many times for proofing. 4 Absolutely prohibit all non-standard operations that are done in order to over-pursue the effect when proofing, such as increasing the concentration and viscosity to increase the hue, adjusting the pressure, scraper to increase the ink transfer rate and so on. 5 Ink must be mixed before use, especially spot color inks. 6 Spot inks that are self-provisioned must be accurately recorded and recorded for future reference. 7 Try to reach the normal printing speed when proofing. 8 If conditions permit, after confirming the basic color of the sample, first print a certain amount of product (such as a roll of film), then sample and confirm it as a standard sample, and keep it as a file. 9 After confirming the standard sample, the connected 2~3m should be taken as the equivalent standard sample, and it should be properly stored in a place with no heat source or ultraviolet light, and the cut part of each print should be used as a sample after printing.

4. Common troubleshooting 1 dirty version: In the plastic gravure, the non-printing surface of the roller often has a layer of resin (a pigment entrained in the resin) on the non-printing surface, which is transferred to the substrate and is stained like a sheet. Or appear linear dirt, this is a dirty version. In addition to the hardness of the blade, the blade pressure, the blade contact angle, and the quality of the plate cylinder, the resulting dirty plate phenomenon is also related to the viscosity of the ink. When the printing viscosity is too high, resins, pigments, and other substances have poor fluidity and cannot be uniformly dispersed and accumulated, causing the blade and the plate cylinder to be damaged under high-speed operation, resulting in linear fouling. At the same time, since the resin and the like are also in a supersaturated state, a large amount of resin accumulates together and under the pressure of the doctor blade, the resin adheres to the drum (the pigment is entrained in the resin) due to the affinity of the resin to the drum, and the sheet becomes contaminated. In general, the smaller the ink printing viscosity, the less likely the dirty plate problem occurs. 2 inaccuracy: Mainly due to the deviation of the diameter of the gravure cylinder; the deformation of the image due to incorrect plate loading; uneven tooth spacing between the shafts, large or small gaps, or overprinting due to top teeth; thin film opening Reel tension control is uneven or uneven gravure film thickness, lotus leaf edge; uneven pressure between the plate cylinder and the impression cylinder at both ends or multi-color overlay printing pressure between the printing plate is inconsistent.

3 Size deviation: Insufficient or excessive shrinkage margin. Due to the influence of the tension of the plastic film and heat drying, the longitudinal dimension of the film changes greatly during printing. Control measures: Adjust the printing tension appropriately to prevent dimensional deviation due to improper temperature setting. 4 Reverse printing (ie, biting): Inverse printing means that the ink of the previous color is overprinted onto the latter printing plate in the overprint. Cause: The ink of the previous color was not completely dried; the pressure of the second color was too large, or the speed was too fast, or the hot and cold air was bad; the substrate had poor printability. Improve the adhesion of the ink of the previous color, adjust the viscosity of the ink, increase the amount of hot and cold air, increase the drying speed of the ink, slow the speed of the Vehicle, increase the ink supply of the latter color, reduce the viscosity of the latter color, and correctly arrange the color sequence of the printing plate; Reduce impression cylinder pressure, or use a softer rubber roller. 5 Albino: The resin is insoluble and precipitated; drying is too fast. Control measures: Re-inking, appropriate slow-drying solvent. There are many problems in gravure printing. In the actual printing operation, the main reason should be carefully analyzed. It can be considered from the aspects of register control, tension control, ink control, temperature control, etc., and quickly eliminated to ensure smooth production. This requires skilled technology, timely understanding of the causes of the above common quality problems, and decisive measures to solve the problem of gravure quality of plastic film in a timely manner. 6 pattern line incomplete: hot air is too large, the ink is easy to dry, the ink is drying too fast in the mesh line, the ink is solid on the surface of the printing plate; the pressure between the printing plate and the impression roller is too small; the angle of the squeegee is not ideal, The pressure on the layout is not enough; uneven unevenness of the printing plate or white spots, shallow printing plate, burr, ink adhesion; ink is too thin; printing speed is too slow. Add butanol in a timely manner to clean the printing area; adjust the pressure; adjust the angle of the squeegee and the pressure on the plate; deepen the printing plate to remove burrs; properly add the original ink; adjust the printing speed.

7 Chromatic aberration: Chromatic aberration refers to the color difference between rolls and rolls during the printing process. Cause: The viscosity of the ink is not well adjusted; the gravure cylinder blocks the plate; the printing staff does not perform properly. 8 block version: printing, with a large number of solvent evaporation, ink viscosity increases, easy to dry inside the network cable; printing process, the location of the scraper blade away from the printing roller or angle is not reasonable, the size of the roller diameter or plate roller into When the depth of the ink tank is not enough, the hot air blown from the drying pipe affects the drum surface, which can cause serious blockage; the ink is mixed with impurities; the engraving depth of the platen roller line is not suitable; when the temperature is too high, the solvent in the ink volatilizes quickly. . The process of gravure printing plastic film is more difficult to control, so in the printing, we must sum up some experiences to obtain our own quality control method.