Discussion on properties of steel barrel sealant
Xiaofeng Qi, director of Zhuzhou City Superstar New Material Factory
At present, the sealant used in domestic steel drums is basically a viscous colloid using rubber as the main material. Although there are differences in appearance and content, there is not much difference in the overall composition. Generally speaking, the sealant for steel drums should contain the following components: rubber elastomer; rubber vulcanization system; inorganic filler material; emulsion stabilization system; viscosity modifier. Of course, individual products also include redox rust inhibitor systems, pigment systems, and the like.
In order to make the barrel manufacturers more aware of the performance of the sealant and better use the sealant, the following is a brief description of the performance and function of the different components of the sealant:
1, rubber elastomer
This is the most important part of the sealant. You can choose natural latex or synthetic latex. You can also mix the two in a certain ratio. Natural rubber latex has good elasticity and cold resistance, and it has good process performance. It is non-toxic and non-polluting. It is the material of choice for most steel barrel sealants. However, in the past three years, the performance of both imported and domestic natural latex has been extremely unstable, mainly due to the phenomenon that the strength is rapidly decreased after the cooperation. After the film is formed, the sealant is broken and may be broken if it is slightly deformed, which may cause leakage of the steel drum. Fortunately, this accelerated change process only exists in the sealant liquid. After the film is formed, the sealant does not show a rapid decline in strength after being placed for two years. Therefore, the sealant manufacturer must strengthen the quality control and control of the sealant. The manufacturer can adjust the formula by detecting the degree of vulcanization of the raw materials, and strengthen the regular inspection after the product leaves the factory. The manufacturer also needs to strengthen the test two months after the purchase time. In the unconditional factory, the simple test method can be used to draw the dried sealant test piece (thickness uniform) on a one-centimeter scale and stretch by hand. The elongation at break exceeds 300% and can be used continuously. However, synthetic latex basically does not have such problems, but the synthetic latex has poor cohesive force, and is easily dispersed during the spraying process, resulting in waste. In addition, the synthetic latex film forming ability is also slightly worse than the natural latex.
2, rubber vulcanization system
This is a part of the barrel manufacturer that is difficult to understand intuitively. Natural latex and most synthetic latexes are linear molecular structures, which are easily dissolved in solvents such as gasoline, toluene, turpentine, and thinner materials commonly used in steel drums. Therefore, it is necessary to add a vulcanization system during use to crosslink the molecular chains to form a network structure and improve the solvent resistance. The vulcanization of rubber can generally be carried out at a temperature above 1000C. Although the sealant is vulcanized indirectly during the phosphating and baking process, the degree of vulcanization is difficult to achieve the required degree, and the safety of the sealant is still used. There will be an impact. For small factories without heating measures, it is a major safety hazard. Therefore, when the sealant is selected for the vulcanization system, the room temperature vulcanization system is used, and although the crosslinking density of the vulcanization is not achieved, the solvent resistance of the sealant can be greatly improved. After the sealant is dried and formed into a film, it is generally placed in 7 days to achieve the best effect of room temperature vulcanization. This is also the case that the steel drum that the manufacturer just produced may leak when loading thinner or other solvent, and the steel drum is placed after a few days. The same solvent does not cause leakage. There is also a rubber anti-aging system that must use a medical grade phenolic anti-aging agent. Although the amine anti-aging agent is cheap, it is reported to have the possibility of carcinogenicity and is discarded as much as possible. Even if a steel drum prepared by vulcanized rubber-based sealant is contained in eucalyptus oil, epoxy chloropropene, or a solvent having a diene conjugated structure, dissolution and leakage are highly likely to occur. The solvent immersion test can be used to test the solvent resistance of the sealant. The manufacturer can use the dried test piece, after being smelted at 100 ° C for 40 minutes or placed for 7 days, immersed in the solvent of the test, after 48 hours, if the test piece is found completely Loss of elasticity, broken or mostly dissolved at the touch of a cylinder, the steel drum made of the sealant is not suitable for containing such a solvent.
3. Inorganic filler
Inorganic fillers have three main functions: (1) reducing the drying shrinkage of the sealant. After the natural latex is dried, the shrinkage rate is above 22%. The sealant is prepared by using pure natural latex to be applied to the R tank of the steel drum cover, and will shrink and fall off after drying. (2) Improve the solid content of the sealant, the solid content of the natural latex is 60%, and the synthetic latex content is generally about 50%. The addition of the inorganic filler can greatly increase the solid content of the sealant, improve the drying speed of the sealant and fill the dry after filling. degree. (3) The addition of the inorganic filler can also appropriately increase the temperature at which the sealant is resistant to baking. Of course, inorganic fillers also reduce the material cost of the sealant. The choice of inorganic fillers varies from one household to another. The filler with low activity and large specific gravity can be added more, and the drying speed is also faster, but it is easy to sink to the bottom, and it is difficult to stir evenly after sinking the bottom. Due to the excessive amount of the bottom filler, the strength of the sealant is low and the leakage rate of the steel drum is increased. If the irregular shape light filler is used, the bubble generated during the preparation process is not easy to eliminate, and the drying speed is slightly slow due to the water absorption effect, but it is not easy to settle. It is easy to stir evenly after being placed for a long time, and the utilization rate of the product is high, and it is not easy to cause the leaky barrel. . The addition of inorganic fillers will inevitably lead to a decrease in the strength of the sealant and a decrease in the elongation, and the amount should be controlled within the range that satisfies the strength requirements of the sealant.
4, emulsion stability system
The filler and vulcanization compound added to the latex must greatly reduce the stability of the latex. It is necessary to add an emulsion stabilizer. Because the emulsion stabilizer can reduce the tensile strength and elongation of the sealant within a certain range. The long rate, while too much stabilizer, the drying speed of the sealant will also decrease. Therefore, the amount must be controlled.
5, viscosity modifier
It is difficult for the sealant to use a chemical thickening method to adjust the viscosity. At present, the sealants used in China are physically thickened by water-soluble polymers. Therefore, the sealant can reduce the viscosity by adding pure water, and increase the viscosity of the sealant by increasing the amount of the thickener. The aqueous thickener can improve the colloidal stability of the sealant by increasing the water film thickness on the surface of the sealant particles and reducing the particle motion.
Other aspects, such as redox system, can effectively control the rust phenomenon at the sealant coating. It has a certain effect on improving the quality of steel drums. The addition of pigments is thicker for 200 liter steel drums. If the defects are easily visible to the naked eye, the application is of little significance. If inorganic pigments such as iron oxide red and carbon black are used, the sealant steel is used. The influence of the contents in the barrel is not great, but if organic pigment is used, it may affect the quality of the contents in the steel drum due to the extraction of the solvent.
When the sealant is used, the technical parameters of the solid content, viscosity, elongation at break, etc. are several technical parameters that must be mastered by the user. The solid content of the sealant determines the amount of sealant used in each steel drum, and the solid elastomer after the sealant is dried. Each barrel manufacturer has different crimping techniques, and the core size of the seven-layer crimping center will also have a large difference. But basically the diameter will be within 3mm, the dry glue volume is 6-13cm3, the amount of sealant can be roughly calculated. The sealant is a thixotropy viscous fluid that will decrease in viscosity at elevated temperatures or rapid agitation, and vice versa. Therefore, during the use of the same batch of sealant, the spray effect will be different with the change of temperature. The manufacturer can adjust the viscosity of the sealant by changing the spray pressure or using pure water to achieve the desired spray effect. If the sealant thickener is not properly selected, it will also slowly degrade. The viscosity of the sealant will also gradually decrease, and even affect the performance of other aspects of the sealant, which needs to be properly handled by the sealant manufacturer.
The strength of the sealant will gradually decrease with the storage time due to the exclusion of the raw material itself and the improper formulation. Foreign product standards, the tensile strength regulations are very different, and for the elongation at break, considering the deformation caused by steel drum collision and fall, the control is basically above 300%. For sealants that exceed the shelf life, the barrel manufacturer should communicate with the sealant manufacturer in time, generally after adjustment.
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