As a method of manufacturing composite materials, the basic characteristics of dry composite are as follows: firstly, the base materials are compounded with adhesives (adhesives) in the "dry" state, and the main processes are as follows: (1) preparation of substrate; (2) preparation of glue solution; (3) coating; (4) drying (drying); (5) compounding; (6) cooling and winding up; (7) curing (curing).
In dry compounding, due to the negligence of production preparation and production management, some technical conditions fail to meet the production requirements, resulting in the quality decline of the composite products produced, which can not meet the user's requirements. In light of the occurrence of secondary and waste products, the production cost will increase; in serious cases, users will be lost, and even economic compensation will occur, resulting in legal disputes. Therefore, the following precautions are listed for reference in order to prevent accidents in the bud.
1、 Precautions in the early stage of production
1. When the adhesive and film are moved from the warehouse to the workshop, the dust, garbage and water drops on the surface of the adhesive and film shall be completely wiped off with a rag.
2. The name, batch number, manufacturer (or supplier) and usage amount of adhesive, base material and diluent used shall be recorded in the daily report.
3. In winter, when the storage temperature is lower than 20 ℃, the adhesive should be transported to the workshop in advance to keep the liquid temperature around 25 ℃. If necessary, it can be put into the curing room for preheating. If the liquid temperature is too low, the viscosity of the glue will increase, the coating amount will be uneven, and the wettability of the film will be poor, which will often be the cause of poor appearance. In addition, poor wettability leads to an increase in coating amount, resulting in an increase in production costs. In the factory, the most suitable temperature of adhesive is 20 ℃～ 25 ℃.
4. In summer, due to high air humidity (especially rainy days) and high temperature, ethyl acetate is easy to absorb water and volatilize; the curing agent is also easy to absorb water and produce chemical reaction, which consumes a part of curing agent, resulting in improper proportion of main agent and curing agent in the prepared glue solution, which makes the adhesive layer dry and the composite fastness is not high. Therefore, in summer should be less with, more glue, with good glue should be used up as soon as possible. In addition, after compounding the glue, the packing barrel with main agent, curing agent and ethyl acetate should be sealed and sealed to prevent water absorption and volatilization.
5. According to the requirements of the specification, the correct concentration of the compound glue should be prepared and determined according to the requirements. The correct steps of glue preparation should be as follows: first weigh the main agent, then add the required ethyl acetate into the weighed main agent, and then fully stir in the same direction for more than 5 minutes, then add the required curing agent, and then fully stir in the same direction for more than 5 minutes, and check the color and foreign matters. After the bubbles completely disappear (about 5-10 minutes), it can be used. Some workers because of the busy work or trouble, simply mix the three materials together, and then simply stir a few times, even if it is finished, so the preparation of glue is very dangerous.
6. Determine whether the liquid humidity and viscosity of the glue are consistent with the data in the manual (generally, the second management is performed by using a tea cup). In case of inconsistency, check whether there is a problem with the preparation ratio or whether the adhesive quality has changed.
7. Make sure that the mixer circulation tank, circulating pump, glue tank and coating roller are free of foreign matter adhesion. Gel or foreign matter should be removed immediately.
8. In order to prevent the volatilization of ethyl acetate in the mixer circulation tank and glue liquid tank, it is better to use pet or PP plate transparent material.
9. Filter (such as nylon socks) should be installed at the return port of the circulating tank.
10. If the coating roller is not cleaned with ethyl acetate, it should be cleaned with plate washing solution once or twice a week to prevent the plate from blocking and reducing the amount of glue. The cleaning method should be carried out according to the instruction of plate washing solution.
11. The relationship between the coating roller and the coating step: generally, after the roller is used to 3-5 million meters, it should be re chrome plated to maintain the normal coating step.
12. Check whether the scraper and coating roller keep normal angle and whether there is scratch.
13. Inspection of the substrate: 1) the surface of the substrate should be smooth and flat, without rigid block or excessive black and yellow spots, crystal dots, etc.; 2) the surface tension of the coating should be between 40 and 44 Mn / M; 3) the average error of film thickness should be within 10% (1 meter width), and the thickness measurement method is to use micrometer caliper. (4) the average error of film thickness should be distributed evenly and unevenly, even if the average error of film thickness is less than 10%. (5) the elongation under composite tension should be less than 1%.
2、 Precautions in the production process
1. The glue solution poured into the glue tank is exposed to the air, coupled with the high-speed rotation of the glue roller, and the glue liquid is stirred. After a period of time, the ethyl acetate will volatilize and the glue concentration will be increased. Especially in summer, it is necessary to test the viscosity of the glue liquid in the circulating tank once an hour. If the viscosity rises, use ethyl acetate to adjust to ensure the same delivery volume. For the glue tank without circulating equipment, the change of glue concentration should be monitored frequently.
2. Compound speed: according to the shape of the coating roll, the maximum processing speed of the flat roll is 180m / min and that of the concave roll is 120-150m / min under the condition of ensuring the glue loading. In the actual production, the compound speed should be determined according to the design requirements of the equipment, the precision of the equipment, the type of the coating roll, the working concentration of the glue solution and the type of the base film. On the premise of ensuring product quality, the higher the compound speed, the higher the production efficiency.
3. The drying temperature of drying channel is generally set as follows: the first section (inlet) is 50-60 ℃; the second section is 70 ℃; the third section is 75-80 ℃; but this is not classical. The general principle is: according to the heat resistance of the substrate, the linear speed of the base film when compounding, and the type of solvent used, the residual amount of solvent after drying should be controlled below 10mg / m2 (Japan and the United States require less than 5mg / m2). If the substrate used is PETP, Pt, OPA with high heat resistance, and the composite speed is high, the temperature of drying channel can be increased accordingly. But we can not blindly pursue drying and increase the temperature of the drying channel, so that the base film shrinks and deforms due to high heat. Generally speaking, under the action of a certain operating tension, the transverse shrinkage of the base film is generally less than 2% after heating by the drying channel. If the shrinkage rate of the base film is large, the temperature of the drying channel can not be set too high. If there is too much residual solvent, the compound speed should be slowed down, the operation tension should be reduced, and the exhaust air volume should be increased to ensure that the residual solvent does not exceed the standard. In addition, due to the use of the compound machine in some factories for too long and no timely maintenance, there is often a phenomenon that the readings of the temperature gauge and the actual temperature do not match. Such equipment can not guarantee that it is qualified for drying, so it should be checked frequently and repaired in time.
4. For composite packaging materials with special requirements, such as cooking bags, wine bags, salad oil bags, etc., the glue loading amount should be calculated to ensure the required glue amount and make the composite fastness meet the special requirements of the packaging materials.
The method of measuring the glue amount is: after the base film is just compounded, cut off a piece and weigh it, then peel it off, remove the adhesive, weigh it, and then calculate the glue amount according to the area. At the compound roll, silicone grease is used to compound the film. The calculation of glue loading is the same as above (this method is suitable for thin film).
5. Tension control: in dry compound, tension control is very important. If the tension is too small, the product is easy to produce
Wrinkle; excessive tension, large stretch, damage to the printing pattern, may also break the film.
The tension control of various substrates can be calculated according to the following formula:
Total tension n = film thickness (mm) × width (mm) × coefficient × 9.8
In general, the tension of OPP is 49-78.4n and that of pet or PA is 78.4-98n
The unwinding tension of LDPE in front of composite roll is 29.4-49n, while that of aluminum foil is lower, about 29.4n
The winding tension of the composite film is 98-117.6n. The tension is controlled by magnetic powder tension controller or friction plate.
3、 End of production phase
This section is about the problems in curing (curing).
It is a problem that every composite packaging factory has to face that the composite materials should be aged. Some color printing factories are busy with production tasks, sometimes the products are not aged or the aging time is very short, which is very unscientific, and often results in the quality decline of products, and even secondary and waste products.

The curing time indicated in the instruction manual of most adhesives is the shortest time required for the curing of composite materials (the temperature of curing chamber is 50-60 ℃). If this time is not reached, the product will not be fully aged. Only after fully aging, the main agent and curing agent of the two-component polyurethane adhesive can fully carry out chemical reaction, and the molecular weight of the two-component polyurethane adhesive can be doubled to form a network cross-linking structure. In this way, the composite material can have higher composite fastness, better heat resistance and stability against medium erosion.

The chemical reaction of two-component polyurethane adhesive will be carried out slowly at low temperature (such as room temperature), but the speed is not fast. It will take 7-10 days to reach a more complete degree, which is not feasible in industrial production. The curing cycle at room temperature is too long, the efficiency is too low, and the final peel strength is not as good as that under heating.
For composite packaging materials, the aging temperature and time are only related to the amount of glue, but not directly related to the substrate. The larger the amount of glue, the longer the curing time is required under the condition of constant curing temperature. As for the relationship between curing temperature and time: when the temperature is 50-60 ℃, the curing time is more than 48 hours, at 70 ℃ it is only 24 hours, and at 80 ℃ it is only 6-8 hours. When the aging temperature is too high, some plastic film will produce shrinkage deformation, even serious to the point of adhesion, and it is not convenient for people to get in and out. Therefore, in most cases, the curing temperature should be set at 50-60 ℃. Only when the automation condition is good and the film is a high temperature resistant material, it is suitable for high temperature rapid curing.
The above is the polyurethane adhesive with high solid content and low viscosity. For the two-component adhesive with low solid content, due to its high molecular weight, the formation time of network cross-linking structure is short. Therefore, the curing time required for compounding with this adhesive is short. Please refer to the product manual for details.
Dongguan Beite packaging materials Co., Ltd. - located in Dongguan City, the world's manufacturing city, is a subsidiary of Beite packaging (China) Co., Ltd., with a plant area of 6000 square meters. It is a flexible packaging enterprise integrating R & D, production and sales. It has a complete set of domestic advanced production equipment, a scientific and humanized management system and a group of experienced technical personnel For backing, to provide customers with quality products and first-class service.
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