Coating application technology
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Coating technology is widely used in the coating and composite packaging of packaging printing, paper, photographic film, film, aluminum coil and other substrates, and with the continuous development of science and technology, the application field of coating technology is more and more extensive. For example, a functional optical film layer in a flat panel display (FPD) and a coating of a lithium battery electrode. At present, coating application technology has been highly valued by relevant technical personnel such as technology and production. However, many printing and packaging machinery companies in China provide less coating methods, which brings greater limitations to the actual search for suitable coating equipment. . Regardless of the coating method chosen to complete the coating requirements, the key part is the coating head. Therefore, this paper combines several common coating methods to explore the coating application technology, focusing on the application performance of the coating head. , thus providing some technical information for the application of coating technology.
1. Anilox roll gravure coating
The anilox roll gravure coating is suitable for low-concentration, high-drying solvent-based adhesives with a smooth coating and no leak coating. The anilox gravure coating apparatus mainly employs a textured (concave-eye) coating roll for sizing coating. The coating effect in this coating mode is uniform, and the coating amount is relatively accurate, but the coating amount is difficult to adjust depending on the anilox roller used. When coated with an anilox gravure, the amount of coating is mainly related to the depth of the ophthalmic roller and the accuracy of the type of glue. The deeper the depth of the concave surface of the anilox roll, the greater the amount of glue transferred from the concave eye to the substrate; conversely, the shallower the depth of the concave surface of the anilox roll, the amount of transfer to the substrate is correspondingly reduced. Too much viscosity and too small viscosity is not conducive to the normal transfer of glue, the viscosity is easy to transfer, too thin is easy to flow, so that the glue is not uniform, easy to produce vertical or horizontal flow pattern. With the application of coating technology in the fields of flat panel display, optoelectronic products, lithium batteries, etc., the micro gravure roll coating process has gradually developed. The micro gravure roll coating process technology is a proprietary technology developed by Japan Kangjing Seiki Co., Ltd. based on the common reverse gravure roll coating process. This coating process also uses the gravure roll mesh line number and the cell depth to determine the liquid content. The biggest difference between the micro gravure roll and the ordinary anilox roll gravure coating process is “micro”. The normal anilox roll has a diameter of 1 2 5 ~ 2 5 0 m m , and the micro gravure coating roll has a diameter of 20 mm and 50 m. The contact area of the micro-gravure roll with the substrate to be coated is small, a part of the coating liquid is transferred to the substrate to be coated, and a part remains in the groove of the gravure roll. Moreover, the micro-gravure roll coating process does not have a compacted back roll, so it is relatively stable when entering and leaving the coating zone, thereby facilitating the improvement of the quality of the transfer coating. Figure 1 and Figure 2 show the conventional anilox roll gravure coating and micro gravure coating roll coating, respectively.
2. Slot extrusion coating process
Conventional extrusion coating refers to hot melt adhesive extrusion coating. This coating process mainly applies solid glue to the substrate and is sprayed directly onto the substrate by a coating die. Hot melt adhesive coating does not require drying equipment and low energy consumption; hot melt adhesive is 100% solid rubber component and does not contain toxic organic solvents. Ordinary sizing coatings use toxic organic solvents (such as toluene, etc.) to dilute the glue, and the toxic gases caused by them are extremely harmful to the operator.
At present, the slot extrusion coating process has been widely used, and is not limited to the extrusion coating of hot melt adhesive coating liquid. The principle of the slit extrusion coating used now is to first input the coating liquid into the liquid distribution chamber of the slit coating die, and then pass through the lateral homogenization at the slit to form a liquid film at the outlet lip. Spread to the coated substrate. This is a pre-measured coating method, that is, the coating amount depends on the ratio of the input liquid amount to the substrate running speed, and precise setting can be made in advance to control the required coating amount. The uniformity of the coating effect of this coating process mainly depends on the coating die, especially the design of the front and rear lip, the processing precision, the deformation state, and the rheological properties and surface tension of the coating material itself. The state of the liquid distribution chamber. Figure 3 is a simulation of the strip extrusion coating.
Figure 3 is a simulation diagram of strip extrusion coating
3. Light roller coating process
The coating of the smooth roll is usually carried out by two-roll transfer coating, and the gap between the top roller and the coating roll is adjusted to adjust the amount of coating. The structure of the entire coating head portion is relatively complicated, and the processing precision and assembly precision of the rubberizing roller, the coating roller, the traction roller and the scraper are required, and the cost is relatively high. When coating with high-precision light roller, the coating effect is better. The coating amount is adjusted by the gap between the rubber roller and the blanket roller, and can be flexibly controlled by the micro-motion adjustment of the coating blade. The cloth has high precision.
The smooth roll coating is divided into a smooth roll coating and a reverse roll coating. In the smooth roll coating, the coating roller rotates in the same direction as the substrate advancement, and the substrate has an elastic back roll support. In the reverse roll coating, the direction in which the coating roll rotates is opposite to the direction in which the substrate of the elastic back roll moves. Roller coating is an ancient coating method that uses less than a reverse roller. The smooth roll coating has high precision, and the reverse roll coating uses precision coating rolls and bearings, and the resulting coating is almost better than any other method.
In the photo-roll coating, since the rubber roller used in the coating apparatus is corroded by the solvent in the coating liquid, the matching between the coating rubber roller and the coating liquid is a key point of the roll coating. Commonly used materials for coated rubber rolls are nitrile rubber (N B R ), polyurethane rubber (P U ), EPDM (EP D D), silicone rubber (S I L I C O N E ). Each rubber has its excellent properties and its insurmountable defects. The advantages of nitrile rubber are that it is resistant to oil, heat and water. The disadvantages are poor resistance to cold and ozone, low strength and elasticity, poor acid and alkali resistance, and poor resistance to polar solvents. The advantages of polyurethane rubber are good wear resistance, high strength, good elasticity, excellent oil resistance, ozone resistance and aging resistance. The disadvantages are poor water and alkali resistance, aromatic hydrocarbons, chlorinated hydrocarbons and ketones, esters and alcohols. The solvent is poor. EPDM rubber has the advantages of anti-ozone, UV resistance, weather resistance and aging resistance. It is the first in general rubber. It has good electrical insulation, chemical resistance and impact resistance. It is resistant to acid and alkali and polarity. Solvent; The disadvantage is that the self-adhesiveness and mutual viscosity are poor, and it is not easy to stick. The advantages of silicone rubber are high temperature resistance, low temperature resistance, ozone resistance, atmospheric aging resistance, and large chemical inertia. The disadvantages are low mechanical strength, poor oil resistance, solvent resistance, acid and alkali resistance, difficulty in vulcanization, and high price. Since the A C agent usually contains a polar solvent, the rubber roller should preferably be ethylene propylene diene monomer. According to the process requirements, the hardness of the rubber stamping roller is generally selected from Sauer A 7 0 ~ 7 5 . Figure 4 is a process flow diagram of reverse roll coating in roll coating.
Figure 4 is a flow chart of the reverse roll coating in roll coating
The above are several coating methods which are widely used at present and have better application effects. In the application of coating equipment, there are also slope coating, curtain coating, blade coating and spray coating, etc. The field of application is also worthy of attention. In the coating process, the glue is often uneven, which requires a certain scraping mechanism to evenly scrape the glue. The scraping mechanism mainly includes a stainless steel scraper, a comma scraper, a scraping bar, a wire scraper, an air jet scraper, and the like.
1 Stainless steel sheet scraper uses a soft stainless steel sheet, so the scraping rubber is not very uniform. Most of the scraping rubber used on the anilox roller is also used for pre-scraping of the coating of the smoothing roller.
2 Comma-type scraper is made of round steel with good strength and hardness. The straightness error of the cutting edge is small. Pneumatic and fine-tuning mechanism can be used to adjust and control the position of the scraper. The coating quantity control and scraping precision are high, and the use is also extremely high. Convenience. Because of its uniformity of squeegee, it is suitable for precise squeegee coating on smooth rolls.
3 The scraping bar is usually made of a round bar with good strength and hardness. When the glue is scraped, the round bar is required to rotate. It is mostly used for the pre-slurry of the pre-coating of the optical roller. When the viscosity of the glue is large, it can also be directly scraped on the substrate with a scraper as a precise squeegee of the coating mechanism. It can also be used for coating a thicker disposable squeegee.
4 Wire scraper is made of high-precision cold-drawn round steel and tightly wrapped around stainless steel wire. It is generally only used for the pre-squeegee coating of the smoothing of the smoothing roller. The precise scraping of the comma-type scraper is needed behind.
5 The air squeegee mechanism acts on the sizing roller by the uniformly ejected airflow, which serves the purpose of squeegeeing, and requires the airflow to be evenly distributed over the entire width of the glazing roller. This squeegee is mostly used for scraping fluidity. glue.
In summary, the coating technique in each case requires selection of a suitable coating method depending on the number of coating layers, wet coating thickness, viscosity (rheology), desired coating accuracy, coated substrate, and coating speed. Coating can be said to be the basis of the entire publishing industry. Paper for reading can be applied and calendered to improve strength and improve ink performance. Printing offset printing plate aluminum plate, coating of sensitized coating on ester plate, and photographic film, color film, photographic paper and coating product of tape and video tape which gradually fade out of people's eyes. At present, coating technology still plays a key role in the printing and packaging, medicine, automotive, clothing, electronics and other industries. Moreover, with the development of coating on-line detection and coating fluid rheology adjustment technology, the innovative coating system is gradually applied to the precision coating of electronic component production, electrodes, lithium ion battery separators and the like.