Improvement of traditional sealing glue for steel drum
Shanghai Xugong Coating Technology Co., Ltd. Xu Guoxing
In recent years, steel drum products have developed rapidly, especially multi-purpose steel drums and various internal coatings.
The application of steel drums has spread throughout the petroleum, chemical, pesticide, light industry, construction, food and other industries.
Most of the objects packed in closed steel drums are liquid, so their sealing performance has received increasing attention. In addition to the quality of the steel, the seam welding process and the crimping technology, the most important factor affecting the sealing performance of the steel drum is the steel barrel sealant.
Since the 1930s, Mobil Oil Company has opened the first domestic steel drum manufacturing plant in China, China's steel drum manufacturing industry has more than 60 years of history, but the steel barrel sealant has been used in the 1930s. Gelatin plus brown sugar composition. Until a few years ago, some steel drum manufacturers switched to other sealants such as natural latex. Although decades of history have proven that gelatin brown sugar sealant is highly adaptable to the contents of steel drums and economical, however, due to the lower melting temperature of the gelatin brown sugar composition, the steel drums containing liquid products are in the summer sun. When the steel drum user fills the hot liquid material, the sealant melts and flows, which causes leakage of the steel drum.
Then, whether it is possible to improve the melting temperature of the gelatin brown sugar composition by some improvement measures, even if it does not melt or melt, a series of tests prove that the answer is affirmative.
First, a simple solution of gelatin brown sugar composition
The sealant composed of gelatin brown sugar for steel drum is made by dissolving gelatin in water at a certain ratio, then adding brown sugar to stir evenly, and then aging. The steel barrel sealant prepared according to this ratio has good elasticity at room temperature, has certain mechanical strength, is ideal for chemical and solvent resistance, and is hygienic, non-toxic, low in cost, quick in curing, small in volume change, and excellent in sealing at normal temperature. . So after more than 60 years, there are many steel drum manufacturers in use. However, its outstanding defect is that it melts in the heat and causes the steel drum to leak.
Second, improved testing and analysis
The steel barrel sealant composed of gelatin brown sugar, the brown sugar in its component only plays the role of plasticizing and antiseptic, gelatin is the key component of the sealant. Therefore, to improve this sealant, it is necessary to work hard on gelatin.
1, the relationship between gelatin freezing force and sealant melting temperature
The raw materials of gelatin are animal skin, bone, tendon and ligaments. Due to the difference in raw materials and production process and quality, its freezing force and viscosity are different. The higher the freezing force and viscosity, the better its quality. Generally speaking, the viscosity is proportional to the freezing force.
It has been found through experiments that the higher the gelatin strength and viscosity of the gelatin used, the higher the melting temperature of the sealant. By using high-temperature gelatin, the melting temperature of the sealant composed of gelatin brown sugar can be increased, but when the gelatin of the gelatin used is higher than 160BL00M. The rising curve of the melting temperature of the sealant becomes flat. Moreover, the gelatin of domestic products as a product has a maximum freezing capacity of only 200 BLOOM (G). Therefore, by increasing the gelatin freezing force, the melting temperature of the sealant is increased, and the range is extremely limited, and the maximum temperature is not 70 °C. Well, it seems that only in the gelatin molecular structure to find a way.
2. Coupling test
As mentioned above, the raw materials of gelatin are the skin, bone, tendon and ligament of animals. The collagen in these raw materials is purified and primaryally hydrolyzed and processed to obtain gelatin. and so. Its main component is of course the natural protein, and the amino acid is the basic structural unit of the protein. Moreover, most protein tables have 20 different amino acids. However, almost all of the amino acids constituting the natural protein have the L configuration type a, that is, the a-amino acid. All oxyacids can be represented by one and the same general formula. The amino acids are condensed (dehydrated) between the various amino acids by the head and tail, that is, the amino group of the former amino acid and the amino group of the latter amino acid. It is called a peptide. Since its structure is chain-like, its structure is called a peptide chain (or a polypeptide chain). This is the simplest structural form of a protein molecule. In this structure, there is an amino terminus in each peptide chain, and an amino group is present in the long chain of each peptide chain, and the nitrogen atom in the amino group has unexposed excess electrons, which is associated with metal ions. Chelation offers the possibility.
The potassium sulphate was formulated into a certain concentration, and added to the already melted gelatin brown sugar sealant while stirring, and the stirring resistance was increased immediately after a few seconds. And soon the sealant became solid and could not be stirred up. After cooling, it was baked in an oven at 100 ° C for one hour without softening, and then placed in boiling water for two hours, and no dissolution was observed. This is the result of the formation of a chelate between the amino group on the peptide chain of the gelatin protein molecule and the chromium ion.
It was found in the experiment that the formation of such a chelate was very fast, and if the potassium chromate added was sufficient, the gelatin brown sugar sealant immediately formed a hard solid block with almost no elasticity, and of course it could not be sealed. Glued. However, if the potassium sulphate as a chelating agent is added too little, the effect of increasing the melting temperature of the sealant is not significant. Therefore, if the melting temperature of the gelatin brown sugar sealant is increased by chelation, its addition amount and the manner of addition are key. l
3. Cross-linking test
In the chelation test, because the formation rate of the chelate is too fast, there are certain difficulties in the actual production process, so an organic substrate with several active groups is considered as a crosslinking agent and gelatin. The protein in the brown sugar composition was subjected to a cross-linking test. Such a crosslinking agent is viscous acid or dichlorobutenoic acid and chloric acid.
It has a more active carboxyl group, an aldehyde group, and a chlorine group, and these reactive groups can react with an amino group on a protein peptide chain. These reactions are actually carried out almost simultaneously, even on the same chloric acid molecule. As a result, the protein peptide chain forms a multi-crosslink with the viscous acid and becomes a three-dimensional network structure.
It was found in the experiment that the crosslinking reaction with viscous chloric acid appeared to be slower than the chelating reaction. The thickening began only after 5 minutes at 95 ° C, and gradually became an elastomer after about 15 minutes, and its elasticity was better than that of the chelate. This may be due to the linear molecules formed by the reaction of the carboxyl group of the viscous chloric acid with the amino group in the protein peptide chain in the network of the crosslinked compound. These factors create favorable conditions for the actual production of steel drums.
Five kinds of gelatin brown sugar sealing chambers with different amounts of chloric acid were added to the oven and the cross-linking compound formed by viscous chloric acid was placed in an oven. After being kept at 100 ° C for one hour, it was found that the least part of the added chloric acid had softened. The rest remain as they are. After placing the five samples in boiling water for two hours, it was found that the least two portions of the added viscous acid had dissolved. Soften in sequence, soften slightly and remain as it is. This means that similar to the chelate, the amount of chloric acid used is critical. If the amount of viscous acid is too large, the crosslinked compound is less elastic; if the amount of chloric acid is too small, the melting temperature of the crosslinked compound is not increased enough.
Third, discussion
Steel barrel sealant made of gelatin brown sugar, due to the inherent deficiency of its composition. There are defects in heat fusion, but it has been proved by experiments that this defect can be overcome. However, whether it is a chelation method or a cross-linking method, there are still some problems.
First, if a chelation method is used, there is a problem that the reaction rate is too fast. Even if the problem of non-cure before spraying is solved in the actual production, the steel drum in the roll of the person is quickly solidified, which causes the curl to be unsealed, and even the problem that the roll of the roll is broken.
Second, if a method of crosslinking using viscous acid is used, it is necessary to solve the problem of spattering of the viscous acid solution during the spraying process. Today's coilers are mostly splashed when spraying gelatin brown sugar sealant. If the gelatin brown sugar sealant is splashed on the body, there is no hindrance, but if it is splashed with chloric acid, it will burn. In addition, it also has a corrosive effect on the equipment.
Third, the steel barrel seal formed by the combination of gelatin and brown sugar is non-toxic, so the steel barrel using the sealant can hold items such as grain, oil and food. Once a chelate or cross-linking compound is formed, whether it is still hygienic and non-toxic, it is still subject to food hygiene inspection.
Fourth, whether it is a method of chelation by chromium ions or a method of crosslinking with chloric acid. There are still some difficulties in using actual production. Because in actual production, gelatin brown sugar is sprayed to the bottom of the steel drum at the high temperature molten state. At this melting temperature, if potassium chromite or viscous acid is added in advance, the gelatin brown sugar sealant forms a chelate or crosslinker and becomes an elastomer state, so that it cannot be sprayed. Therefore, in order to make gelatin brown sugar sealant overcome the defects of heat fusion by the method of chelation or cross-linking mentioned in this paper, and successfully applied to actual production, it is necessary to make two sets of each other at an angle so that An injection device that allows the two liquids to be sufficiently mixed in space after being ejected. Moreover, firstly, the injection quantity of the two should be accurately proportional, and secondly, the air mixing between the two liquids after the ejection and the winding of the steel barrel body and the bottom cover on the winding machine must be uniform. Otherwise, it will result in a seal ring composed of the entire sealant. In some places, the chelation or cross-linking is sufficient to cause the part to become hard and the sealing performance is lost. In another place, due to chelation or cross-linking, even There is no sequestration or cross-linking, and there is still the problem of melting with heat.
Therefore, a steel barrel sealant composed of brown sugar gelatin, which has the drawback of suppressing heat and melting, can be chelated by the use of chromium in potassium sulphate as described herein, or by viscous acid. The method of the joint is solved. However, this is only a test result, and efforts must be made if it is to be applied to the actual production of steel drums.
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