Exploration on Improving the Sealing Packing of Steel Barrel
In recent years, steel drum products have developed rapidly. In particular, the application of multi-purpose steel drums and various internal coating steel drums has spread to petroleum, chemical, pesticide, food and other industries.
Closed. Most of the items packed in 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 affecting the sealing performance of the steel drum, another important factor is the sealing packing of the steel drum.
In the early 1930s, since Mobil Oil Company opened its first steel drum manufacturing plant in Shanghai in Shanghai, steel drums have been around for more than 60 years. The sealing filler of steel drums has been based on the formulation of brown sugar and gelatin in the 1930s. Since the melting temperature of gelatin is only about 65 °C, coupled with the high temperature degradation of water during the preparation process and the plasticization of brown sugar, the actual melting temperature of this filler is only about 50 °C. If the gelatin viscosity used is below 7E (15% 40 ° C) and the freezing force is less than 250 BLoom (g) (12.5% 10 ° C), its melting temperature is lower. When the gelatin Engler viscosity 4.3E (15% 40 ℃), when the gel strength 113BLoom (g) (12.5% 10 ℃), brown sugar, gelatin, water in a ratio of 12:10:18 formulated filler 37 It will flow when °C. Thus, in high temperature weather or when the steel drum user fills the liquid at a high temperature, the brown sugar gelatin filler melts in the bead of the steel drum, causing leakage.
It takes a long time for the steel drum to be used from the production to the user's use, plus the entire use of the product after filling the product. In this process, after high temperature and sun exposure, the long chain of gelatin will inevitably degrade or the gelatin will be spoiled, which will further reduce the melting temperature of the brown sugar gelatin filler, and its performance will also deteriorate. .
Under the situation that the requirements for packaging containers are getting higher and higher, all steel drum factories have recognized the necessity of improving brown sugar gelatin filler. To improve the sealing of the steel drum, it is necessary to understand the basic requirements of the steel drum for the sealing packing.
The author believes that, first of all, the sealing filler of the steel drum should be an elastic body with a certain mechanical strength. In this way, the filler can produce a "bomb" seal within the bead of the barrel. Most fillers can meet this requirement. Therefore, when using hard and brittle organic polymers as steel drum fillers, additives such as plasticizers and foaming agents and some soft monomers are often added for copolymerization. It has a certain mechanical strength and elasticity. For example, plasticizers added to polyvinyl alcohol (PVA) include glycerin, polyethylene glycol, sorbitol, polyamide, urea derivatives, etc., while vinyl acetate (VAC) can be used not only in dibutyl phthalate ( DBP) acts as a plasticizer to increase flexibility and can also be used to increase flexibility by copolymerization with butyl acrylate (BA). Incidentally, the copolymerization of VAC and BA also improves the polar solvent resistance of VAC. In addition, while these hard and brittle organic polymers increase flexibility, some suitable blowing agents may be added to enhance the elasticity. Moreover, during the foaming process, the filler can be more fully enriched into the gaps in the bead. In this way, the sealing performance of the steel drum is further enhanced. Of course, the preferred blowing agent is preferably of the closed cell type such that the contact area of the filler with the bead is large, facilitating filling and sealing.
Second, the steel barrel sealing packing should have good chemical and solvent resistance. In this way, the steel drum will not leak due to the dissolution of the sealing packing when filling different chemicals and various solvents. The contents of the steel drum will not be contaminated by the dissolution of the filler.
Sealing fillers are only solvent and chemical resistant. Sealing fillers resistant to all chemicals and all solvents are not present. In fact, there is a different opinion as to whether the steel barrel sealing packing will come into contact with the liquid in the steel drum or it will be completely dissolved by the internal liquid after contact. Japan's Asian Sub-Products Co., Ltd. believes that: "The filler is deeply applied to the edge of the barrel and the bottom and the cover, and is sealed by crimping. Therefore, in general, these fillers are not in direct contact. The contents of the steel drums"o Bugess.son (Abingdon) Ltd. also mentioned in the British patent "Metal Containers and Their Manufacturing Methods and Equipment": "Because the bottom of the bucket, the lid and the barrel are kept The joint of the metal is such that the filler does not substantially contact the contents of the container." Therefore, the steel drum sealing filler used by Japan National Semiconductor Co., Ltd. is styrene-butadiene latex. It is well known that styrene-butadiene rubber is soluble in aromatic hydrocarbons and is not completely soluble in gasoline, chloroform and the like. However, U.S. Patent 3,736,893 believes that. Since the winding between the bottom of the bucket, the lid and the edge of the barrel cannot be free of voids, the contents of the steel drum will contact the filler. . According to the existing manuscript technology in China, it is difficult to completely prevent the filler from being in contact with the contents of the steel drum. However, the contact of the filler with the contents of the steel drum is not likely to be soaked. At best, only the contents of the steel drum are infiltrated into the filler from the crimping gap. Therefore, steel drum fillers need to have good chemical and solvent resistance, but their requirements are not necessarily very demanding. In fact, many units currently use natural latex as the main component for steel drum filling, while natural latex is mainly composed of isoprene cis polymer, soluble in benzene, solvent gasoline, carbon disulfide, tetrachlorination. Carbon, chloroform, etc. It has been proven that the sealing performance of such steel drum fillings is still possible.
In fact, some steel drum fillers currently used can increase their solvent resistance by chemical means such as copolymerization, crosslinking, and grafting. For example, in order to improve the water resistance of polyvinyl alcohol, it can be crosslinked. After cross-linking, it no longer dissolves. It can be cross-linked; sodium sulfate, zinc sulfate, ammonium sulfate, potassium alum, boric acid, polybasic organic acids and aldehydes. The solvent resistance of styrene-butadiene rubber can be improved by grafting carboxyl groups. Further, the water resistance and the like of the polyvinyl acetate can be improved by copolymerization with butyl acrylate as described above.
Third, the steel barrel sealing packing should have good aging resistance and high temperature resistance. We manufacture steel drums that are used throughout the country and even abroad. The temperature difference of the environment in which the steel drum is placed is very large, and the temperature of the filling liquid is also different. Therefore, the sealing packing of the steel drum is required to be not melted at a high temperature, and is not embrittled at a low temperature, and always maintains a certain elasticity. We have used brown sugar gelatin for sixty years, because it needs to be improved because it melts at a slightly higher temperature. So, can it be improved? The answer is of course yes.
Gelatin is a protein obtained by cooking the skin or bone of an animal. It is a linear polymer composed of α-amino acids bonded by peptide bonds. The α-amino acid generally has a group such as -OH, -SH, -SCH3, -COOH, NH2 or the like. By cross-linking with chloric acid (OHC-C(CL)-C(CL)-COOH) and potassium sulphate [CrK(S04)・12H20], we have a promising result: boiled in the laboratory Insoluble for two hours. After being used as a filler, a 200 liter steel drum was introduced into a 100 ° C flood house, and no melt was oozing out for one hour. In the case of a 200 liter steel drum with uncrosslinked ordinary brown sugar gelatin as a filler, at 650 C, the melt oozes out after 15 minutes. Of course, there are problems with the amount, concentration, addition method and addition time of the added wattle. The dosage is large, the concentration is high, and the cross-linking is easy to occur, so that the brown sugar gelatin hardens and loses the elastic amount and the amount is too small, the concentration is too low, and the effect is too little, or the effect is too small. The method of addition depends on the method of application (spraying and manual application). Adding time is important, especially when spraying with brown sugar gelatin, be sure to synchronize with the spray point. The artificially glued ingredients must be mixed with additives while applying. If added earlier, brown sugar gelatin gradually solidifies in the container.
Fourth, as a sealing filler for steel drums, it should be hygienic and non-toxic. Because there are many users who use steel drums to hold cooking oil, honey, and other edible liquids, it is important to pay attention to the hygienic condition of the filling materials. Although the effect of the filler on the contents of the 200 liter steel drum is extremely small, even only in PPM, it is not intended to lower the hygiene standards, but within the scope of the hygienic standard, the filler should be considered. cost.
Fifth, the way and conditional factors of the sealant sizing should be considered. At present, the sealing methods of the sealing fillers of the various barrel factories are different. In general, however, it is nothing more than spraying on the crimping machine, or by applying a sealing filler on the bottom of the bucket and the cover, and then curing or partially curing the upper crimping machine and the barrel. In practice, we have realized that brown sugar gelatin is not convenient for manual coating, and natural latex is easy to block the nozzle when spraying. Therefore, the sealing filler should take into account the sizing process.
Regarding the sizing process, the author believes that it is ideal to apply the glue on the crimping machine. Because of the pre-coating, after the filler is cured or semi-cured and then wrapped with the barrel, the filler loses fluidity, it is difficult to ensure that all the gaps are filled. If it is pre-coated by hand, the filler will inevitably become uneven and will affect the sealing effect of the crimp. When the edge is sprayed, since the filler is a liquid at this time, the filler is filled with the crimping force, and under the action of the crimping force, the entire gap of the curl is filled. Of course, this requires the sealing filler to solidify or heat and solidify in the bead of the steel drum. I have used natural latex as a test, and I rolled it on the side. After baking at 1700C, I saw that the natural latex did not cure. If the curing is not cured, of course, the sealing effect is not ideal, so it is best not to use the edge curling process.
There are many sealing fillers that meet the above requirements. In addition to the currently used, the author believes that hot melt adhesives and plasticized plastics are also ideal for two steel barrel sealing fillers.
The hot melt adhesive is composed of a thermoplastic polymer material such as an ethyl acetate resin, a polyester resin, a polyurethane resin, a tackifier, a plasticizer, a wax, an antioxidant, a filler, and the like. In the heated and molten state, it has fluidity, and after being wetted by the surface of the object to be coated, it solidifies as soon as it is cooled. This is the same as brown sugar gelatin. In fact, brown sugar gelatin is also a hot melt adhesive, but the melting point is too low.
The hot melt adhesive has a solid content of 100%, no solvent, no water, and little change in volume between liquid and solid states. Due to the difference in thermoplastic polymer materials and additives in hot melt adhesives and their formulations, their performance is quite different. After testing, the author believes that the hot melt adhesive used for sealing the steel barrel has a melting temperature of 120-130 ° C. The melting temperature is too low, which is likely to cause leakage of the steel drum. Since the hot melt adhesive has no obvious melting point, the hot melt adhesive having a melting temperature of 120 to 130 ° C starts to soften at 80-100 ° C. Excessive melting temperatures can cause nozzle clogging and excessive energy consumption. The test proves that the properties of the hot melt adhesive with a reasonable melting temperature of 120-130 ° C are ideal, which can fully meet the above five requirements. However, it is necessary to solve the problem of plastic coating equipment and insulation facilities.
Plasticized rubber, the actual application of more PVC resin. Large molecular weight polyvinyl chloride has excellent chemical resistance. High strength, good shock absorption performance, also has the advantages of wear resistance, noise reduction and cheaper price. Moreover, the polyvinyl chloride resin may also be non-toxic hygienic. In general, the higher the molecular weight of polyvinyl chloride, the better its chemical resistance. Its main disadvantage is its poor thermal stability. It can cause different degrees of degradation by high temperature above 140 °C, but it can be overcome by heat stabilizer, anti-aging agent and various other additives. Polyvinyl chloride resin can be used in steel drum sealing packing by a variety of additives.
The steel barrel sealing filler polyvinyl chloride plasticizing glue is a viscous liquid mixture in which a selected polyvinyl chloride resin is suspended in a liquid plasticizer. Its spraying and painting properties are good. In the steel drum bead, it is baked at 170 ° C and 10 minutes, that is, plasticized into a flexible sealing material. In order to meet the five conditions mentioned above, in addition to the special choice of polyvinyl chloride resin, plasticizers, anti-aging agents, lubricants, foaming agents, fillers, paraffin, methyl silicone oil, etc. must be strictly selected.
Polyvinyl chloride plasticizer is very suitable for the process of spraying on the crimping machine. The mushroom must be the original crimping machine using brown sugar gelatin. Just remove the heat source and use PVC plasticizer with a little adjustment. This plasticized gel is a viscous liquid at normal temperature. The desired viscosity can be obtained by adjusting the formulation.
On the crimping machine, at the same time of crimping, a plurality of quantitatively oriented spray plasticizing glues are set by the glue spraying mechanism. In this way, it fills the entire seam of the curl. When crimping, the pressure roller and the steel drum are rubbed to the side to generate a certain amount of heat, so that the plasticized plastic is pre-plasticized, so that it has a preliminary sealing performance. Then, after baking at 170 ° C for 10 minutes, it is completely plasticized. By adjusting the formulation, the plasticizing temperature can be lowered, and the baking time can be further shortened. Of course, plasticized rubber is only suitable for units with post-baking conditions.
At present, there are many kinds of steel barrel sealing fillers, and the performance is not the same. New varieties are under development, some sealing packings are of good quality, and some are not ideal. What kind of standards should be met in the sealing material of steel drums, and it has not yet been unified. The five requirements put forward by the author are not necessarily comprehensive, at least there is no quantitative requirement. The author calls for the development of steel drum seal packing standards as soon as possible in order to improve the quality of the packing and further improve the sealing performance of the steel drum.
