At present, the dry-type compound method is generally used for the boiled bag.
1. Selection of the amount of glue
Standard sizing amount range: 2.8 ～ 3.2gsm. Excessive sizing amount has no meaning for peel strength, but increases drying load. For compound equipment with insufficient drying capacity, it increases the probability of delamination and bag breaking after cooking.
When testing the amount of glue, pay special attention to the change in water content before and after the nylon film passes through the drying tunnel, which affects the accuracy of the detection of the amount of glue!
When we produce boiled bags, we can not only look at the amount of glue, but also pay attention to the microscopic uniformity of the adhesive coating. The parameters of the screen roller will directly affect the microscopic uniformity of the adhesive coating.
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2. Moisture requirements of ethyl acetate
GB / T3728-2007 has clear requirements for the moisture content and ethanol content of ethyl acetate. The unqualified quality of ethyl acetate (such as moisture content and alcohol exceeding the standard) often leads to wrinkle quality accidents of the composite film.
Table 1 is the ethyl acetate moisture content test data of a flexible packaging factory. Among the 20 batches of incoming inspection, 4 batches exceed 500PPM (excellent products), one of which is unqualified, and the batch is in barrels (distributed Distributors) solvents, other batches are tank truck solvents. Most small flexible packaging companies purchase drummed solvents. The moisture content in ethyl acetate is likely to exceed the requirements of qualified products.
The alcohol content in ethyl acetate often does not attract the attention of most flexible packaging companies. One flexible packaging company's ethyl ester detection data (barreled solvent) found that only one superior product and two first-class products in 14 batches, overall The quality is poor and the soft pack factory should pay attention.
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3. Ensure that the adhesive is dry enough
We usually only pay attention to the amount of compound glue. In fact, insufficient drying is often the most direct cause of incomplete curing of the adhesive (insufficient heat resistance of the adhesive layer), delamination and wrinkling quality of the packaging bag when it is boiled. There is a small amount of water and alcohol impurities in the prepared glue solution. Good drying property can make the water and other impurities in the glue layer volatilize as much as possible, reducing the consumption of the proportion of curing agent in the glue layer. In order to ensure that the adhesive is fully dried during dry compounding, pay attention to the following points:
(1) The drying performance of the equipment itself, such as the air intake and exhaust volume of the equipment and the length of the oven.
(2) Setting of drying temperature.
①Set the drying temperature in the first zone. The drying medium in the first zone has the highest ethyl ester concentration, so the drying temperature in the first zone cannot be set too high (generally not higher than 65 ° C). Because the temperature is too high, the solvent on the surface of the adhesive layer volatilizes quickly and the skin is instead inhibited the escape of the inner layer solvent in the drying section of the latter areas.
â‘¡Dry temperature gradient setting. The temperature of the oven should be set according to the law of the gradual increase of the gradient, the purpose is to accelerate the diffusion and volatilization of the solvent of the adhesive layer in the hardening zone and the elimination of odor zone, and reduce the solvent residue in the film.
(3) Adjustment of air intake and exhaust.
â‘ In the drying process, the intake and exhaust air volume valve should be opened to the maximum, and the return air valve should be closed.
â‘¡In the dry hardened area and odor elimination area, the return air volume can be increased appropriately, which can save part of the energy consumption.
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4. The influence of environmental temperature and humidity
The high-temperature and high-humidity season in summer is a frequent time period for the quality accident of the dry-composite double-layer polyurethane adhesive dry layer. According to an adhesive factory, 95% of the quality feedback received in summer is not dry with the adhesive layer related. Under the environment of high temperature and high humidity, the water content in the air is very high, and it is easy to consume the curing agent through the volatilization of acetic acid and acetic acid into the rubber tray, which makes the ratio of the main agent of the adhesive and the curing agent unbalanced, resulting in the compound after curing. The cross-linking and curing of the layer is not complete, and the phenomenon of delamination and wrinkling occurs when boiled.
Flexible packaging enterprises that do not have conditions to control the temperature and humidity of the workshop should pay attention to the following points in the high-temperature and high-humidity season in summer:
â‘ By detecting the temperature and humidity of the environment and the temperature above the rubber tray and the solvent tank, the "dew point" phenomenon is avoided. Once the "dew point" appears, it means that a large amount of moisture in the air enters the rubber tray, and the glue layer is prone to dry.
â‘¡ The boiled bag should be compounded as far as possible in the high humidity period during production arrangement.
â‘¢ The ethyl acetate barrel and glue circulation barrel used for compounding should be covered and sealed. If a semi-closed rubber plate is used, the influence of environmental humidity can be further reduced.
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5. Aging process requirements
General curing conditions: temperature 50 ～ 55 ℃, 48 hours.
In addition, we should also pay attention to the uniformity of the entire film roll curing: â‘ Show whether the temperature is consistent with the actual value near the film roll (the actual temperature of the film roll up, down, left, and right); â‘¡ Whether the air near the film roll can achieve effective convection; Effect of temperature on curing: There is a certain process of heat transfer, and whether the curing conditions of the wound core composite film meet the requirements. (This may be a major cause of unstable quality.)
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