1. Base material. The main raw material constituting the sealant is called the base material. The base material has a great influence on the sealing effect of the adhesive, especially the medium resistance of the sealant mainly depends on the choice of the base material. Therefore, the base material is mainly composed of polymer synthetic resin and synthetic rubber or natural polymer organic matter. The main requirements of the steel drum sealant for the base material are:
(1) The material of the docking steel drum and the medium of the steel drum contents have good chemical stability;
(2) It has certain strength and viscoelasticity after film formation;
(3) It has good adhesion and wettability to the sealed joint of steel plate;
(4) The temperature range is wide, and the change of viscosity with temperature is small;
(5) Good aging resistance and long-term use;
In fact, many sealant formulas are composed of several high-molecular materials, they make up for each other's defects, give full play to their respective strengths, so that the sealant achieves the best sealing effect.
2. Plasticizer. The main function of the plasticizer is to increase the plasticity of the base material. It is a non-volatile compound, so it requires good affinity with the base material, good migration resistance and excellent solvation. The specific requirements of plasticizer for steel drum sealant are:
(1) Can dissolve most polymer materials;
(2) Low volatility;
(3) Good thermal stability;
(5) Good medium resistance;
(6) Low mobility.
The amount of plasticizer added has a certain limit, if the amount is too large, it will affect the heat resistance and pressure resistance of the sealant.
3. Filler: The filler can increase the viscosity, adhesion and deformation of the base material, can improve the thixotropy and heat resistance of the rubber material, reduce the difference in the thermal expansion coefficient of the sealant and the joint surface, and play a role in reinforcement The effect of adding fillers can also reduce costs. The type of filler, particle size, shape and amount of addition, etc., have a greater impact on the performance of the sealant, so it must be properly selected when used, and its requirements are;
(1) Inactive, with good chemical stability;
(2) Does not contain moisture and oil;
(3) Uniform particle size;
(4) High heat resistance;
(5) Good dispersion;
(6) It has good thixotropy and wettability to the base material. The amount of filler varies with the type of base material. For the same base material, the reinforcing effect of various fillers is also different. Therefore, the amount of filler should be properly used according to the different base materials. At the same time, it is also related to its own type, shape and particle size, and the ability to adsorb the matrix component, most of which are selected through experiments.
4. Solvent. Sealants are usually divided into two types with and without solvent. The addition of solvent can dissolve the base material, improve the construction performance, facilitate the application and make the sealant easy to fill the depressions and gaps of the joint surface, thereby making the joint surface connection more tight. At the same time, the addition of solvent can also dissolve the oil stain remaining on the joint surface, making it and the sealant penetrate into one body, thereby preventing leakage caused by the oil stain. The choice of solvent is generally determined according to the type of base material. At the same time, it has certain limits and requirements on the volatility, compatibility, dosage, toxicity, and flammability of the solvent itself. Generally, low-boiling point, low toxicity, non-flammable and explosive, good miscibility mixed solvent is the solvent of sealant, its content in the glue solution is 10% to 40%.
5. Other additives.
(1) Stabilizer: The sealant is mainly made of synthetic resin or synthetic rubber, which is prone to aging during the use of light and heat, which reduces the performance of the sealant. Agent. There are many types of stabilizers, and all kinds of stabilizers and antioxidants for rubber and resin can be used.
(2) Colorant. In order to make the various sealants easy to distinguish from each other, the sealants need to add colorants. Colorants are generally dyes. When selecting, we must consider the water resistance, heat resistance, oil resistance and chemical resistance of the colorant to avoid discoloration or contamination of the packaged material due to heat.
(3) Anti-precipitation agent: During the storage process of the sealant, relatively dense fillers and pigments are prone to precipitate, which makes the sealant layered and uneven, which affects the use; to prevent this phenomenon, you can add anti-precipitation Precipitant, Taiwan fumed silica, etc., can properly absorb high-density fillers, pigments, etc. A
(4) Anti-caking agent: if the sealant contains a solvent with a low boiling point or a high volatility, the coating will evaporate too quickly after the coating, which will cause a skin on the surface, which will hinder the volatilization of the solvent inside the adhesive layer, resulting in the sealant The sealing performance is reduced.
(5) Desiccant: The sealant is a viscous substance, the solvent is not easy to volatilize quickly, therefore, the drying time increases. In order to accelerate the evaporation of the solvent, a drier can be added if necessary. The driers are mostly cobalt, manganese, aluminum and other vaporized compounds. In addition, there are borate, fatty acid soap, naphthenic acid soap, etc., which is commonly used is cobalt naphthenate. A
(6) Spices: Sealants generally contain solvents, and some high-molecular organic substances also have some special odors. In order to improve the irritancy of solvents and components, fragrances can be added appropriately. The selected spices are required to be soluble in organic solvents. The amount of fragrance depends on the type and amount of solvent, and is generally 0.2% to 2%.