Can sealing compound (1)
Shanghai Xugong Coating Technology Co., Ltd. Xu Guoxing
Technical field
The present invention relates to a sealed tablet having a good filling effect, and in particular, the present invention relates to an improvement of a main component constituting a sealing compound such as styrene-butadiene latex, and the sealing compound of the present invention can effectively prevent metal at a portion of a can body The etch of the exposed surface of the slit.
Background technique
In the production of the metal can, when the sealant is applied, the liquid mixture called the sealed substrate is embedded in the annular groove of the can bottom cover, and the annular sealing layer of the sealing compound is formed by drying. Then, the bottom lid of the can is rolled up and integrated into the can body to form a whole can.
The main component of the sealing compound in the present invention is styrene-butadiene latex. Such a sealant made of a tackifier, a filler, an emulsifier or a dispersant, and a thickener and styrene-butadiene latex can be widely applied to the sealing requirements of metal containers.
The main component of the general sealing compound, styrene-butadiene latex, consists of styrene-butadiene latex particles with a diameter of 1200-1500. When such a known sealed substrate is coated with a pump at a relatively low speed of 20 to 150 reciprocations per minute, a satisfactory result can be obtained. However, we have found that when we coat the bottom lid with a relatively high speed of, for example, 180 to 400 reciprocations per minute, the sealing performance and other qualities of the seal coating are less than satisfactory.
More specifically, the above-described sealing compound emulsion undergoes mechanical friction when it is sprayed toward the can bottom cover annular groove by the adjusted releasable leak-proof needle valve and nozzle. As the mechanical friction increases, the number of impacts per minute of styrene-butadiene latex particles increases, and the resulting problem is that the temperature of the sealing compound increases.
During the usual sealant spraying process, as the mechanical friction increases and the temperature of the glue increases, the coagulated agglomerates in the glue increase. At the same time, the viscosity of the glue also increases. Therefore, a high-speed or long-term continuous sealant spraying process can cause a decrease in the adaptability of the sealing compound. As a result, the sealing performance and quality of the sealant layer are lowered.
Further, it has been found that when the above-mentioned sealing compound emulsion is sprayed on the annular groove of the can bottom cover, the outer edge of the bottom cover is rusted. Since surface metallized steel sheets such as tin plating and chrome plating are applied to metal containers, the corrosion resistance of these surface coatings effectively prevents corrosion of the steel surface. However, on the outer edge of the bottom cover, the steel substrate is completely exposed, and the contact of these steel substrates with the sealing substrate causes corrosion.
If rust occurs, then the bottom of the tank and the can body are rolled up. These rusts are contained in the sealing compound, which in turn causes decomposition of these sealing compounds, resulting in a decrease in the quality of the seal. In addition, this fibrous rust that occurs in the crimping edge will also cause elongation, resulting in damage to other surfaces of the can. Once the items are contained, it will also cause damage to the contents.
Summary of the invention
It has been found that when the average diameter of styrene-butadiene latex particles is between 1600 and 3000, it can be used as a latex for sealing compounds. As stated earlier, the increase in coagulation agglomerates and other anomalies, as well as the increase in viscosity, is caused by an increase in temperature caused by mechanical friction during high-speed or long-term continuous dispensing. Therefore, as long as the mechanical friction and temperature rise are effectively controlled and the sprayability is improved, abnormal phenomena such as the above-mentioned coagulated agglomerates are effectively eliminated.
After repeated research, we found the cause of the corrosion of the outer edge of the can bottom cover. That is, when some dielectric material, such as sodium chloride, is mixed in the styrene-butadiene latex as a part of the sealed substrate glue carrier to correct the diameter of the latex particles, it can cause rust of the outer edge of the can bottom cover. However, when an alkali metal carbonate or an alkali metal phosphate is used as a dielectric to correct the diameter of the latex particles, the rust of the outer edge of the can bottom cover can be effectively prevented.
We have completed this invention on the basis of the above findings.
More specifically, the center of this invention is to provide an excellent sealing station for metal containers that are compatible with the spray performance and that are resistant to rust. The sealing compound is obtained by adding a suitable dispersing agent or emulsifier, thickener and filler in the styrene-butadiene latex particles having an average diameter of 1600 to 3,000.
Another aspect of the invention, as previously mentioned, provides a conditioning agent for the diameter of the styrene-butadiene latex particles in the sealed station used in the metal container. They are alkali metal carbonates and alkali metal phosphates, which account for 0.3 to 2.0% by weight of the total solids of styrene butadiene rubber. By the way, in the introduction of the usual particles, the more direct and detailed particle size situation needs to be explained by the photo of the emblem. This article omitted the relevant chart for the convenience of description.
research method
In this invention, the average particle diameter of styrene-butadiene latex is between 1600 and 3000, but when the average particle diameter of styrene-butadiene latex is between 1800 and 2800. It is more able to give the sealing compound good filling properties and criticality.
According to the Japanese Industrial Standard Physical Property Test, we draw a graph of the average particle diameter of styrene-butadiene latex and the weight of coagulated agglomerates. Based on the graph, we conclude that if the average of styrene-butadiene latex is compared with conventional compounds. The particle diameter can be controlled within the above-mentioned range, and then the formation of coagulated agglomerates can be significantly controlled.
According to the relationship between temperature and viscosity of styrene-butadiene rubber emulsion, it is considered by research. When the viscosity is between 3000 and 6000 CPs, it is suitable to spray the sealing compound at high speed. The viscosity of a general sealed substrate varies with temperature. When the average particle diameter of the styrene-butadiene latex is within the range given by the present invention, the spray temperature adaptation range of the sealing compound can be significantly expanded.
Within the above range, the present invention improves the physical property stability of the sealing compound and the stability against temperature change by correcting the particle diameter of the styrene-butadiene latex. These two stabilitys are not related to the styrene-butadiene latex itself. The realization of these stability is first achieved by adding a suitable tackifier, filler, thickener, emulsifier or dispersant to the styrene-butadiene latex.
In the physical property stability test according to the Japanese Industrial Standard, as the particle diameter of the styrene-butadiene latex is changed, if the average particle diameter is between 1800 and 3000, the coagulated agglomerates hardly form. The viscosity of the styrene-butadiene latex itself is affected by the temperature. As the temperature increases, the viscosity decreases, but in fact, the viscosity is not affected by the temperature. According to the above facts, it can be easily understood that when styrene-butadiene latex is initially prepared by adding a tackifier, a filler, a thickener, an emulsifier or a dispersant, in the process of high-pressure glue, The physical properties of the latex and the stability to temperature change are declining. However, when the particle diameter of the styrene-butadiene latex is adjusted by the particle diameter adjusting agent, all of the above trends do not exist.
In the present invention, as long as the average particle diameter of the latex is within the range as described above, the styrene-butadiene latex which is specially treated according to any known method can be selected. The preparation of styrene-butadiene latex is generally obtained by emulsion polymerization of styrene and butadiene in an aqueous medium by adding an emulsifier or a dispersing agent. According to the polymerization temperature, it can be divided into two kinds of cold and hot styrene-butadiene. emulsion.
The polymerization temperature of the cold glue is lower than 10 ° C, and the polymerization temperature of the hot glue is between 35 and 70 ° C. Both cold glue and hot glue can be used in principle in the present invention. However, since cold glue contains relatively many polymerization inhibitors, if a cold glue is used, these polymerization inhibitors remain in the sealed substrate. When a sealed substrate made of cold glue is used for a metal container, once the food is loaded, the odor of these foods is affected.
Therefore, it is preferable that the hot glue having an emulsion polymerization temperature of between 35 and 70 ° C is used as the styrene-butadiene latex in the present invention. In order to give the best combination of elasticity and plasticity of the styrene-butadiene latex sealant, the better ratio of styrene and butadiene in the emulsion polymerization is 28:72~55:45, preferably 35:65. ~55:45.
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