At the end of March this year, a unit in the Guangdong region complained to our company about the use of PU-1975A adhesives, which caused a large number of composite products to be scrapped. The manufacturer believes that it is an adhesive quality problem and claims to our company. After conducting inspections in various ways, our company reached the following conclusions:
1. Since February 2004, the unit has successively purchased Huaguang PU-1975A polyurethane adhesive from Zhejiang New Oriental Ink Group Co., Ltd. for a total of 50 sets (1000Kg for the main agent and 200Kg for the curing agent).
2. The quality inspection center of our company conducts sample inspection for batch numbers sent to this unit, and re-observes the composite test samples on the machine before leaving the factory. The product quality is normal and no quit phenomenon occurs.
3. The national standard stipulates the impurity content of water and alcohol in ethyl acetate as a solvent for color printing in flexible packaging. The primary product shall not exceed 0.2%, and the secondary product shall not exceed 0.4% (weight percentage). The ethyl acetate solvent sample used by our company's personnel for adhesives extracted from this unit showed that the content of impurities (methyl alcohol) in the ethyl acetate solvent reached 2.48%, exceeding the standard by 6 times.
4. Our company's technical personnel will come to the company and recommend adopting the same batch of adhesive and ethyl acetate solvent and other equivalent raw materials that meet the standard. Under the same conditions, let the company re-examine the composite test. If the same phenomenon occurs, we Willing to take responsibility, if the composite test does not have this phenomenon is not related to my adhesive.
At the same time, we learned that the adhesives used in this batch of lost products also have adhesives from other manufacturers, and similar phenomena have also occurred. This matter has been fully understood. At the same time, the use of two adhesives and two adhesives have problems at the same time. It is clear exactly what the problem is.
At present, the weather has gradually increased to high temperatures, and the air humidity has also increased significantly. During dry film composite processing, a considerable number of composite color printing manufacturers do not pay attention to this potential change. Naturally there are various quality problems in the process of color printing and compounding. . I think it is necessary to provide high-temperature and high-humidity weather to the composite processing and composite processing of matters to pay attention to the majority of printing complex manufacturers for your reference.
We all know that most of the dry compounding uses two-reaction polyesters and polyurethane adhesives. However, its performance is generally different due to the choice of isocyanate, the molecular structure of the polyester polyol, the degree of polymerization, the functional groups, and the mixing ratio. The two-phase reaction is a cross-linking reaction between a main agent containing a hydroxyl group at a terminal portion of a polymer and a curing agent containing an isocyanate group in a molecular structure, and is combined into a polyurethane having a higher density. The curing agent containing an isocyanate group has a strong activity and reacts with a substance containing a hydroxyl group and an amine group, and the reaction rate is more than 10 times faster than that of a polymer polyester or a polyurethane main agent. Such as methanol, ethanol, water and other amines and other substances. This is also the reason why most polyurethane adhesive manufacturers have restrictions on water and alcohols in the specification.
In the process of dry compounding, the effects on the compounding caused by high humidity are numerous, such as:
1. Insufficient curing of the adhesive, remaining sticky after compound curing, resulting in reduced peel strength;
2. The speed of cross-linking slows down, the initial adhesive force of the adhesive decreases, and the composite film easily causes tunneling;
3, high-temperature cooking film bags, in the high-temperature cooking process bag broken phenomenon;
4, solvent evaporation is not complete, the phenomenon of composite membrane bag odor increased;
5. When the composite foam phenomenon is increased, the composite film can be easily spotted, white spots and crystal spots;
6, the composite film feels stiff and brittle.
Matters needing attention in high temperature and high humidity weather:
Through the above understanding, we have a general understanding of the effects of high-temperature and high-humidity weather on dry compounding. In the dry compounding process, we must carry out targeted control in various processes:
1. We must control various films, such as nylon and cellophane, and when they are creased, they may have absorbed moisture. Therefore, if there is no compound finished, use metal foil or good barrier properties. The film wraps the film on a shelf in a dry environment and should never be piled directly on the floor.
2. We must control the water and alcohol content of the used solvent ethyl acetate, try to purchase the normal channel of solvent, and seal storage. To determine the moisture content of ethyl acetate, a method can be used to determine the moisture content of the ethyl ester by mixing half of the ethyl ester and half of the toluene. If there is a water droplet and a whitening phenomenon at the bottom of the mixture, the ethyl ester has a high moisture content. In addition, fast moisture indicators can also be used to detect moisture content. As for the control of alcohol content, titration methods can be used to detect them. However, the operation is more complicated and requires more reagents. Those who do not have certain analytical experience are difficult to master. But at present, there is no simple and convenient method of identification. I am also trying to find out. If I find it, I will post it in the later published Guangdong Packaging Magazine.
3. We must control the compound environment, place exhaust fans indoors, and strengthen indoor air circulation, but be careful not to blow to the compound machine, and check that there are no beads on the guide roller, composite roller, and roller, and wipe them with a dry towel. .
4, in the preparation of adhesive, the amount of the appropriate reduction, with the use of the distribution, do not place too long, at the same time, to ensure the amount of curing agent to make it as far as possible to the upper limit, increase the main agent and curing agent crosslinking degree.
5, to change the process parameters of the composite machine, currently the majority of the domestic composite machine outlet is small, in the composite, the inlet speed is greater than the speed of the air, so that the formation of high pressure in the drying tunnel, causing the solvent to slow down the evaporation rate, so that after compounding Increased residual solvent in the film. Therefore, the outlet pipe is enlarged, and if the outlet pipe is longer, an induced draft fan should be installed at the outlet of the air outlet. Generally, the imported composite machine has this device. In this way, the air outlet speed is greater than the air inlet speed, so that a low air pressure is formed in the drying tunnel, and it is preferable to volatilize the solvent and reduce the residual solvent. In addition, increase the temperature of the drying tunnel as much as possible (note that the first zone should not be too high - that is, into the film area).
6. When compounding, pay attention to the scraper and guide roller near the glue tank at any time, there is no water bead to produce, and at the same time reduce the speed, because the speed is too fast, the solvent volatilization speed in the rubber tank is easy to speed up, the local temperature near the glue tank is too low, Causes condensation of water vapor.
(author/Xiao Haiyi)
Guangdong packaging