Flexible foil aluminum foil gravure and coating quality analysis

At present, the use of blister packs for the packaging of pharmaceutical tablets and capsules is becoming more and more common. Pharmaceutical blister packs, also known as PTP, are based on pure aluminum foil for industrial use. On medical aluminum foil printing and coating machines, gravure printing techniques and roller coating methods are used to print text patterns on the surface of aluminum foil and apply a protective layer. The bonding process is applied on the other side of the aluminum second. The brief process flow is: aluminum foil unwinding - gravure printing - drying - protective coating - drying - adhesive bonding - drying - foil winding. During the entire production process, the surface quality of the gravure printing text pattern and the heat sealing strength of the adhesive layer are required to be strictly controlled in the process operation. Therefore, the use characteristics of the printing ink and the coating amount of the adhesive layer are used herein. Controls two aspects, expounds how to grasp the characteristics of the aluminum foil ink and analyze the factors and control methods that affect the aluminum foil adhesive coating amount.

First, the characteristics of aluminum foil printing ink

The printing inks used in aluminum foils are mainly divided into two categories. One is polyamide inks. The printing inks have excellent adhesion, dispersibility, gloss, wear resistance, and solvent release properties for printing on various materials. Because of its softness, it is mostly used for the printing of plastic films. When it is used for the printing of aluminum foil as the base material, the excellent performance of the ink can be expressed, and its heat resistance also meets the requirements of aluminum foil printing. . The other type is a complex aluminum foil ink mainly composed of vinyl chloride-vinyl acetate copolymer resin/acrylic acid resin. Its characteristics are bright color, high concentration, especially strong adhesion to aluminum foil, and good transparency. In the selection of pigments, heavy metals and other toxic components are not used, and they are widely used in the packaging of medicines and foods. When using it, you should pay attention to the following issues:

1. Dry changes

The drying of gravure printing inks is accomplished by solvent evaporation, which promotes drying of the ink by the action of heat and wind. The drying speed of the ink should be matched with the printing speed and the drying device and adjusted based on them. When the drying is too slow, the quick-drying solvent or quick-drying retardant can be added to the ink, and the ink can be added when the drying is too fast. Slow-drying or slow-drying diluent.

2. The mastery of ink viscosity

In order to ensure that the ink does not precipitate during storage, generally the viscosity is large, and should be diluted appropriately during printing to achieve the required viscosity and fluidity, depending on the structure of the machine and the printing speed. Generally, the No. 4 viscosity cup is used. The ink viscosity was measured with a machine speed of 20-80 m/min. Viscosity between 22-28 seconds. The more viscous ink, when using a large amount of release agent, should be evenly stirred, so that the release agent is evenly distributed in the ink. Since the temperature and humidity of the room have an influence on the concentration of the ink, it is preferable to use an ink concentration detector to determine the amount of the added solvent, and to measure the density of the ink at regular intervals according to changes in temperature and humidity. When the gravure printing foil is used, if the ink concentration is too low, the printed text pattern will not be bright and the web will be stenciled. If the ink density is too high, cracks will occur at the pattern, which will not only waste ink, but also cause prints. The surface is uneven and not beautiful.

Second, the factors affecting the amount of aluminum foil printing coating and its control

1. The effect of the number, depth and shape of the anilox roller on the coating amount

At present, most pharmaceutical aluminum foil printing and coating equipment use an anilox roller coating device, also known as a wire coating method. The anilox roller is composed of a hole and a net wall. The pit on the roller is usually called a net hole, and the high part is secondarily a net wall or a network cable. The ratio of wall to wall is about 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 using the aluminum foil device for printing and coating, the construction principle and working state of the anilox roller are as follows: when the adhesive is filled in the cells of the anilox roller, the anilox roller rotates when the cell exits the adhesive solution After the surface, the liquid on the smooth surface of the roller is scraped off by a scraper, leaving only the liquid that cannot be scraped off in the concave groove. This liquid adhesive is then brought into contact with the surface of the coated aluminum foil substrate. This contact is This is achieved by the action of an elastic rubber roller, so that a portion of the adhesive solution in the cell is transferred to the surface of the aluminum foil substrate. Since the adhesive is fluid, it will slowly and automatically flow on the surface of the foil. Flat, so that the original borderless liquid becomes a continuous uniform liquid layer. A portion of the liquid in the anilox roller compartment is transferred to the aluminum foil. The anilox roller rotates at the same time. As the roller is immersed again in the adhesive liquid, the liquid binder fills the net. , In this way, an anilox roller with a small diameter can transfer the adhesive solution evenly and uniformly onto the aluminum foil substrate, so that the surface of the aluminum foil can be uniformly applied to the mixture. Obviously, if the screen lines in the anilox roller are smaller per inch and the cells are shallow, the filled adhesive volume is small, and the coating amount is relatively small. The anilox roller has different shapes of cells, and its coating amount is not equal. For example, 200 pyramidal anilox rolls, ie 200 cells per inch, about 8 cells per mm, adhesives The storage capacity is about 0.5 pounds per 1000 square feet, ie 2.4 grams per square meter, while the 24 triangular-threaded anilox roller has an adhesive inventory of 13 pounds per 1,000 square feet, ie 63 grams per square meter.

2. Concentration and density of binder solution versus coating amount

For the anilox roll already prepared in the actual printing and coating, the depth of the cell depth and the number of the network wire have been fixed, and the shape of the cell site is not changed. Under this condition, the coating amount depends on the preparation of the adhesive agent and Concentration and density. We know that the coating amount is the dry film-bonded solid material per square meter of aluminum foil substrate area. Therefore, if the binder solution has a high solid content, the dry film-bonded solid material on the aluminum foil substrate will be much more. , coating more. Therefore, the relationship between the coating amount and the depth of the adhesive cell is: the coating amount is proportional to the depth of the cell and the thick and dense adhesive. If the depth of the cell depth of the anilox roller is fixed in the actual printing and coating operation, the coating amount has a great relationship with the concentration and density of the binder liquid, that is, the size of the coating amount is determined by the liquid concentration. . On the contrary, if the adhesive concentration and density are determined, then the viscosity of the Xia Xia Qiang can be obtained. The effect of the hardness and pressure of the rubber roller in the coating device on the coating amount:

When the depth of the cell and the adhesive [concentration, density are determined, the coating amount of the anilox roller is also affected by the hardness and pressure of the rubber roller in the coating device. The requirement for the rubber roller is that the pressure on the left and right sides should be uniform. That is to say, when the rubber roller is manufactured, the rubber compound of the mixing torch must be uniform and the vulcanization conditions must be strictly controlled, and the quality at any point is the same. If the rubber roller used is very soft, elastic, and the pressure on the roller is large, the amount of coating decreases, and vice versa. This is because the rubber roller squeezes into the depth of the anilox roller pocket under a heavy pressure to expel the adhesive solution out of the rubber roller to reduce the coating amount of the adhesive.

In actual operation, the pressure of the rubber roller to the anilox roller is controlled in the range of 2-3Mpa.

4. Effect of scraper's operation and coating amount in coating device

1) Squeegee pressure

At present, the methods for adjusting the blade pressure device in the device include: tension spring pressure regulation, hand wheel pressure regulation, cylinder pressure regulation and pressure hammer pressure regulation. When cloth is used, the pressure of the doctor blade acting on the anilox roller is too small, and even if the blade is not pressed or mechanical impurities, the doctor blade can be topped up to cause a suspicious gap, so that the coating is uneven and the coating amount increases. The factors that affect the squeegee pressure are: different hard and soft blades, different angles between the squeegee and the anilox roller. In actual operation, the squeegee is used to adjust the scraper. The scraper pressure is generally about 200-400 Kpa.

2) Scraper angle

The angle between the squeegee and the tangent of the anilox roller contact is generally between 15 degrees and 30 degrees. If the angle is too large, the doctor blade is almost against the anilox roller, and the surface of the anilox roller is not smooth. When it runs at a high speed, it will cause the elastic blade to vibrate or jump, causing the solution to be bouncing up, causing the coating to The uneven amount of cloth causes a large difference in coating amount. In addition, too large an angle can easily damage the blade.

3) Sharpness of scraper

The sharpness of the scraper mainly depends on the angle of blade wear and the purity of the solution and the quality of the knife. If it is a new knife, the sharpness of the knife should be to effectively scrape the adhesive layer on the anilox roller without producing a knife. If the sharpness of the knife is moderate, the solution layer can be scraped cleanly from the production site to obtain a uniform coating amount, whereas the difference in the coating amount becomes larger.

4) Flatness of scraper

The degree of smoothness of the doctor blade means that warping deformation does not occur, and the amount of coating is uniform, otherwise the difference in the amount of coating becomes large. The flatness of the scraper depends on the method of installing the scraper. Of course, it may also be related to the foreign matter stuck in the holder groove or on the blade and the lining. Therefore, the lining should be wiped when loading the knife, and then the new knife should be placed behind the lining. Into the tank. Rotary blade back screws should be tightened from the middle of the blade first, then gradually tightened on both sides, and both sides should be tightly rolled. In order to prevent the blade from twisting, it should be completed two or three times to tighten the screw. While turning the screw, clamp the blade and the lining with a piece of cloth, and pull it tightly to one side. The knife thus formed is relatively flat. In order to ensure the difference in the amount of coating within the standard range.

5) Left and right movement of the blade

Scraper moving left and right will play an important role in raising the scraping line, increasing the scraper utilization rate, and reducing the wear of the anilox roller. From this point of view, the wear of the net wall is small, the net is relatively deep, and more fluid is contained in the container, which is beneficial to achieving The amount of coating required.

Third, the optimal coating amount of aluminum foil substrate and adhesive

After the coated aluminum foil is heat-sealed with the PVC hard sheet, the degree of adhesion of the two after heat sealing is usually measured by the heat-sealing strength of the adhesive layer. Is it better to apply the adhesive as much as possible during the printing and coating process? How much is the best adhesion effect? The physical test shows that the heat seal strength of aluminum foil and PVC is proportional to the coating amount within a certain range, but it is not proportional to a certain extent. In most cases, the coating amount is 3-6g/ The cm square can meet the heat seal strength requirements. If the coating amount is increased, the value of the heat-seal strength increases to a certain value as the coating amount increases, the heat-seal strength curve tends to be balanced, and the strength change is small, so it is not necessary to increase the coating amount of the adhesive. It will increase costs.