What is the solution to the problem of rubber molding?

Reasons and solutions for whitening and spraying of rubber products

Whether natural rubber, synthetic rubber, or recycled rubber is used to produce rubber products, the surface of the rubber products may turn white after a period of use, which is what we often call blooming. Why is this? The causes of blooming in different rubber products are different. The inside of the rubber product may cause the deterioration (aging) of the rubber material to turn white due to improper placement or long use time. This whitening phenomenon is a kind of rubber blooming, which is the phenomenon of liquid or solid compounding agents moving from the inside of the rubber to the surface of the rubber. Problems with the raw material compounding agents of rubber products (quality problems) will also cause the deterioration (aging) and whitening of rubber products. Therefore, the formula of the rubber material must be standard, and this phenomenon will occur if there is any inappropriateness. This phenomenon usually occurs mainly due to the following reasons: Improper formulation design Saturation spray: common in sulfur, accelerators, activators, antioxidants; Migration spray: common in processing aids, migratory antioxidants and antistatic agents; Generation spray: common in the use of accelerators and reaction products in sulfur vulcanization systems; Reaction retention: common in the excessive amount of low molecular weight substances in organic peroxide vulcanization systems ; Stress blowout: common in inorganic fillers: such as calcium carbonate; 2. Improper process operation. Uneven mixing causes poor dispersion, and local saturation exceeds saturation. The mixing temperature is too high, causing local over-weighting of the compounding agent. Inaccurate weighing (over-weighing, under-weighing, missing weighing, wrong weighing). The vulcanization temperature is too high, and polymer degradation causes frosting. The vulcanization temperature is too low, resulting in incomplete reaction and insufficient sulfur spraying. The vulcanization time is not enough, resulting in insufficient sulfur spraying. Improper operation of the release agent or mold washing water sprayed causes the rubber surface to turn white. 3. Raw material quality fluctuations due to different origins, different preparation methods, different processes, and different batches of raw materials vary greatly. The synthesis process of raw rubber: differences in polymerization temperature, catalysts, synthetic monomers, etc., cause different solubility. Purity, moisture, ash content, pH value, physical properties, etc. change 4. Poor storage conditions Temperature: The solubility of the compounding agent in rubber generally rises and falls with the rise and fall of temperature Time (pressure\humidity): The pressure, humidity of the surrounding air, and time during storage of the rubber also affect the solubility of the compounding agent, but generally the effect is not significant. However, if the pressure is high, the compounding agent in the rubber of the pressure part will form a crystal nucleus, precipitate on the rubber surface, and form frosting; if the humidity of the air is too high, the effect of the compounding agent with high polarity on the raw rubber (non-polar) will be weakened, and the solubility of the compounding agent will decrease, resulting in frosting; the longer the storage time, the more obvious the frosting on the rubber surface. Since the temperature and humidity of the air in the storage environment vary with the seasons, and the difference is large, it is very easy to cause the solubility of the compounding agent to change, resulting in frosting. 5. Rubber aging Rubber aging mostly leads to the destruction of the complete and balanced network structure of the vulcanized rubber, thereby destroying the chemical or physical combination of various compounding agents and raw rubber molecules and compounding agents in the rubber system, and reducing the solubility of the compounding agent in the rubber system. Therefore, those compounding agents that are locally in an oversaturated state will be freed and precipitated from the rubber to form frosting. Preventive measures: The composition of the frosting on the rubber surface is often complex and rarely single. There is always a primary and secondary distinction in the complex components of frosting, because the compounding agents affect each other in the rubber. As long as one compounding agent is sprayed out, it will destroy the uniformity of the entire compounding agent in the rubber and produce a concentration gradient, which will easily cause other compounding agents to spray out along with the spraying of the previous compounding agent. Therefore, in order to prevent frosting, it is necessary to first analyze the main components of the frosting, and then take measures to prevent it according to the causes of frosting. (1) Use accelerators and antioxidants together: If only one additive is used, it is difficult to achieve the effect if the dosage is too small, and frosting is easy to occur if the dosage is too large. Therefore, several additives can be used together to achieve the effect and reduce the dosage. (2) Utilize the mutual interference and restriction of different compounding additives in frosting: When different additives are used together, sometimes there will be mutual interference and help to inhibit frosting. For example, softeners, ointments, reclaimed rubber, etc. all have this function. In particular, additives with large relative molecular weight can penetrate into the short chain of rubber macromolecules and can effectively adsorb easy-to-spray additives. (3) Understand the upper limit of the amount of easy-to-spray additives, and ensure that the amount of various easy-to-spray additives in the formula is within its solubility range. (4) Rubber mixing storage: The rubber compound must be stored for no less than 8 hours before it is molded to allow the various additives to be fully dispersed. At the same time, it helps to relax the internal stress of the rubber compound and achieve uniform and balanced force. A stable dispersion system can inhibit the external spraying of particles. (5) Ensure that the vulcanized rubber reaches the positive vulcanization state (6) Strengthen the management of finished products, packaging and storage conditions. Finished products should be sealed in plastic bags to prevent aging due to contact with sunlight, oxygen, etc. during storage, and avoid storage at low temperatures.