The key to improving the quality of printing and coating of colored aluminum foil

In the mid-1980s, foreign drugs that were packaged using advanced technologies began to flood into China, and the domestic pharmaceutical market was impacted. At that time, most domestic medicine tablets still used old-style glass bottles and other packaging forms. China's pharmaceutical industry opened the prelude to the replacement of pharmaceutical packaging of various materials, including the use of aluminum foil with superior performance in all aspects. product. We have successively introduced foreign aluminum foil printing and coating equipment production lines to reach the scale production capacity of blister packaging. In the early stage of production, the raw materials for aluminum foil in China were all imported. The annual output was about 400 tons, and most of them were “foil” printed on the surface of aluminum foil without a text pattern. A few products were printed on one side with aluminum foil.

In recent years, the application scope of aluminum foil packaging has been expanding. In addition to pharmaceutical packaging, food packaging, health care product packaging, etc. have been applied, prompting the continuous improvement of China's aluminum foil printing technology, and now can achieve both sides of aluminum foil can be printed on both sides. Not only can print a color of the product, but also can be printed into a variety of multi-color colorful text patterns, aluminum foil surface coated with imitation gold foil and other colors are displayed in front of consumers, this packaging form makes people feel noble Gorgeous, put it down, played a good role in propaganda and protection of products.

Gravure printing color foil

The aluminum foil printing is to print the text pattern through the concave surface of the printing plate roller. First, the printing plate roller is processed into a printing plate graphic by external processing. The graphic part is eroded into ink holes or pits on the surface of the copper layer of the roller. The non-graphic part is the outer copper surface of the roller itself. The plate cylinder rotates in the ink tank, and each ink hole is filled with thin ink. When the roller rotates out of the surface ink tank, the excess ink on the upper surface is the blade installed on the surface of the plate cylinder. Scraping, when the plate roller and the substrate contact with the aluminum foil, the surface of the elastic rubber embossing roller presses the surface of the aluminum foil to the plate cylinder so that the ink in the ink hole is transferred to the surface of the aluminum foil. At this point, the aluminum foil printing is completed. jobs. Since aluminum foil material is different from paper materials and plastics, the key to its printability is to master ink characteristics, ink viscosity, and ink drying degree so as to print a product that meets quality standards and achieves user satisfaction.

Ink and foil printing applicability

Printing inks for aluminum foils are mainly divided into two categories: one is a polyamide ink, which has good adhesion, dispersibility, gloss, abrasion resistance, and solvent release properties for the printing of aluminum foils. Because of its softness, it is mostly used for the printing of plastic film. When applied to the printing of aluminum foil as a substrate, the excellent performance of this ink can be expressed, and its heat resistance can also meet the requirements of aluminum foil printing. The other type is a complex aluminum foil ink based on a copolymer of vinyl chloride and vinyl acetate copolymer, which is mainly composed of grease/acrylic resin. It is characterized by bright color, high concentration, particularly strong adhesion to aluminum foil, and good transparency. , In the choice of pigment, do not use toxic components such as heavy metals, widely used in medicine, food, health products packaging.

Adjustment of the viscosity change of aluminum foil printing ink

The inks suitable for aluminum foil printing have been selected, but the viscosity of each ink is different. The inks used do not precipitate during the storage process. Generally, the viscosity is relatively large. When printing, the ink should be diluted to achieve the viscosity and the viscosity used. Liquidity, which also depends on the structure of the device and the printing speed. The viscosity of the ink is generally measured with a No. 4 viscosity cup, and the printing speed of the machine is between 30 and 70 m/min. Viscosity is adjusted between 25-30 seconds. In the application of larger viscosity inks, the use of a large amount of diluent should be dissolved uniformly, so that the diluent is evenly distributed throughout the ink, due to the indoor temperature and humidity have an impact on the ink concentration, it is best to use the ink concentration detector to determine The amount of solvent is added, and the ink concentration is measured at regular intervals depending on changes in temperature and humidity and printing speed. When gravure is used to print aluminum foil, if the ink concentration is too low, the printed text pattern will not be bright and the web will have a “sticking” phenomenon. Too much ink concentration will cause cracks in the pattern, which will not only waste ink. , And easy to cause the print surface is not smooth, not beautiful.

The degree of ink drying in printing

The drying of the ink in the aluminum foil gravure printing process is accomplished by the volatilization of the solvent, and the ink is dried by the action of the heater and blowing hot air. The degree of drying of the ink should be matched with the printing speed and the drying temperature, and these two basic factors can be adjusted at any time in combination with the indoor temperature and humidity. When the printing speed and drying temperature are constant, the indoor temperature is too low, the ink will dry too slowly on the surface of the aluminum foil, and a quick-drying solvent or a quick-drying diluent may be added to the ink, whereas the ink may be dried too quickly, and an appropriate amount may be added to the ink. Slowly dry the diluent to suit the changes in ambient temperature and humidity during the printing process.

Color aluminum foil coating process

The process of color aluminum foil printing and coating must be composed of a protective layer/print layer/aluminum foil layer/print layer/adhesive layer, but the basic process composition must have a protective coating layer, an aluminum foil printing layer, and a coating adhesive layer. Aluminum foil printing coater to complete. At present, an anilox roller coating device for the coating process of most color aluminum foil printing and coating equipment is also called a wire coating method. The surface of the coated anilox roll used was composed of a mesh and a mesh wall. The pits on rollers are often referred to as nets, and the high part is called a net wall or cable. The ratio of the net to the net is approximately 1:5. After processing, the anilox roller is coated with a hard chromium layer with a thickness of 0.015-0.02 mm to increase the surface hardness of the anilox roller. The hardness value is HRc62-65. When the aluminum foil is coated, the process and the state of the coating roller are: when the adhesive or protective agent used for coating is filled in the cells of the anilox roller, the anilox roller rotates when the cell exits. After the liquid surface of the adhesive (protective agent), the liquid at the smooth surface of the roller is scraped off by a scraper, leaving only the liquid that cannot be scraped in the concave net, and the liquid is then in contact with the surface of the coated aluminum foil substrate. This contact is achieved by the action of a resilient rubber roller so that a portion of the binder (protectant) solution in the cell is transferred to the substrate surface of the aluminum foil due to the fluidity of the adhesive (protective agent). It will slowly and automatically level out on the surface of the aluminum foil, causing the original discontinuous liquid to become a continuous and uniform liquid layer. A part of the liquid in the anilox roller net is transferred to the aluminum foil, and the anilox roller is rotated at the same time, and is immersed in the binder liquid again after one rotation, the liquid binder fills the net hole again. Once again, an anilox roller with a small diameter can uniformly transfer the adhesive solution to the aluminum foil substrate without any problems, so that the surface of the aluminum foil can be uniformly coated with a binder (protective agent). Obviously, if there are fewer network lines per unit area in the anilox roller and the deeper the cell site, the greater the coating amount, the more the number of line lines on the anilox roller, the shallower the cell site, and the adhesive filled (protection There is less agent, and the coating amount is relatively small. In addition, the shape of the cells of the anilox roller is different, and the coating amount thereof is also not equal. For example, 200 pyramid-shaped anilox roller coating, ie 200 cells per inch, binder storage capacity of 24 grams per square meter, and triangular thread-shaped anilox roller, binder stock per square About 63 grams of rice.

The main points of color aluminum foil coating

The main production process of printing and coating color aluminum foil is to use a process procedure of applying an adhesive (protective agent) to the aluminum foil with an anilox roller in the production process of aluminum foil, and evenly disperse the pigments or dyes of various colors to the binder. In the protective agent system, a colorful pattern is formed on the surface of the aluminum foil adhesive layer (protective layer). In order to obtain the correct color required by the user, it is necessary to grasp the amount of adhesive and protective agent applied during the process. This is a very important process indicator. If the adhesive agent is not configured, the coating amount varies greatly or the process The non-standard operation may cause the aluminum foil to be coated with uneven colors and different shades. The adhesion with the plastic hard sheet is not firm. Therefore, problems occur in the coating process, which not only affects the appearance quality of the product, but also affects the inherent quality of the product. In the long-term production practice, the author summarizes the key points to be grasped in the aluminum foil coating process.

1. To properly match the concentration and density of the binder (protectant) solution. For the anilox roll that has been prepared during the process of coating the color aluminum foil, the depth of the cell depth and the number of reticulate lines have been fixed, and the shape of the cell site cannot be changed.

In such production conditions, how much the adhesive (protective agent) is applied to the surface of the foil depends on the adhesive (protective agent)
Formulated concentration and density. We know that the coating amount is the mass (grams) of dry film bonded solid material per square meter of area of ​​the aluminum foil substrate, so the binder (protectant) solution has a high solids content and is coated on the aluminum foil substrate. There are many film-bonded solid materials and the coating amount is large. It follows that the relationship between the coating size and the concentration or density of the binder or protective agent and the depth of the cell is that the coating amount and the cell depth are proportional to the concentration and density of the binder or the protective agent. If the depth of the cell depth of the anilox roll is fixed in the actual process production operation, the amount of coating is determined by the concentration and density of the liquid. If, on the other hand, the concentration and density of the adhesive or protective agent are determined, the amount of adhesive or protective agent applied is determined by the depth of the cell of the anilox roller.

2. Reasonably adjust the pressure value of the coating roller. When the depth of the cell depth and the concentration and density of the adhesive or protective agent are good, the coating amount of the anilox roller is also affected by the hardness and pressure of the rubber roller in the coating device, especially the left and right sides of the rubber roller. The pressure must be uniform. This requires that in the process of manufacturing the rubber roller, the mixing of the rubber should be uniform, the vulcanization conditions must be strictly controlled, and the hardness of the rubber roller should be guaranteed. If the rubber roller used is very soft, the hardness is small and the elasticity is large, and it acts on the roller. If the pressure is large, the coating amount will decrease. This is because the rubber roller squeezes deeper into the anilox roller under a heavy pressure, squeezes a part of the adhesive or the protective agent solution, so that the amount of the adhesive or the protective agent is less. In the actual production operation, the rubber roller pair The pressure of the anilox roller should be controlled within the range of 2 to 3 MPa.

3. Mesh coating scraper tips.

(1) Squeegee pressure value: At present, there are four general methods for adjusting the blade pressure device in aluminum foil printing equipment: tension control pressure, handwheel adjustment pressure, cylinder adjustment pressure and pressure hammer adjustment pressure. During coating, if the pressure of the doctor blade on the anilox roller is small, even if the blade does not press against the anilox roller or there is mechanical impurity on the blade surface, the blade will be topped up to form a gap, so that the coating is uneven and coated. The amount of cloth becomes larger. The factors influencing the squeegee pressure are: the squeegee itself is not the same as the hard and soft; the angle adjustment of the squeegee and the anilox roller is different. When the blade is actually operated, an example of a hammer adjustment blade is used. The blade pressure is generally about 200 to 400 kPa.

(2) Reasonable adjustment of the scraper angle: The angle between the scraper and the tangent of the anilox roller contact is generally between 15 and 30 degrees. If the angle is too large, the scraper is almost against the anilox roller, and the surface of the cable is not smooth. When it rotates at high speed, it will cause the elastic blade to vibrate or jump, causing the solution to be bouncing up, resulting in non-uniform coating amount and causing a large difference in coating amount. In addition, too large an angle can easily damage the blade.

(3) Maintain the sharpness of the blade: The sharpness of the blade mainly depends on the wear angle of the blade and the purity of the solution and the quality of the blade. If it is a new knife, the sharpness of the knife should be such that the adhesive or protective agent layer on the anilox roller can be effectively scraped without generating a knife. With a moderate degree of sharpness of the knife, the solution layer can be effectively scraped off to obtain a uniform coating amount, whereas the difference in the coating amount becomes larger.

(4) Adjustment of the flatness of the blade: The blade is flat and does not warp. In the operation of the scraper, it should be completed twice or three times when the screw is tightened. The screw should be turned on one side and the blade should be fastened with a quick cloth. With linings and hard