（1）Polyurethane roller pre-polymerization preparation
① Dehydration of polyester polyol (in dehydration kettle): polyester with Mn2000 (hydroxyl value 53-59, mgKOH/g, solubility point 40-50℃), heated and melted in stainless steel or enamel kettle with stirring, dehydration temperature 100-140℃ (polyether 100-110℃), vacuum dehydration for 30-60 minutes with residual pressure 5mmHg, so that its water content < 0.05% (dehydration can be observed from the sight glass). In order to make the liquid in the tank fully degas, the stirring device can be turned on and off intermittently, and after pumping vacuum for a period of time, the heating of the reaction tank can be stopped to make the material temperature drop to 70-80℃.
② Prepolymer synthesis (in the reactor); the performance of the product depends on the raw materials used and their ratios and processing technology. Firstly, we select suitable raw materials according to the performance requirements, such as temperature, force and contact medium and service life, and then select suitable ratio and process conditions (such as mixing temperature, pouring and demoulding time and vulcanization conditions) according to the required hardness. In order to ensure the quality of prepolymer, polyester dehydration and prepolymer synthesis should preferably not be carried out in the same kettle, and the prepolymer synthesis reaction should be carried out under dry nitrogen protection. In order to prevent the reaction from violent and rapid temperature rise, cooling device must be provided. It is recommended to add material order: TDI first and then polyester, if the reaction is violent, polyester can be added in stages, so that the reaction process is smooth, the reaction temperature is easy to control, and the content of free isocyanate monomer in the synthesized prepolymer is low and the structure is more regular. Keep it at 80℃, react for 1-2 hours and analyze the isocyanate group content. The prepolymer of domestic and foreign brands that meet the requirements can also be purchased under possible conditions.
(3) Prepolymer degassing (can be done in the A tank of prepolymer synthesis reactor or casting machine); defoam for 30-60 minutes at 85℃ and residual pressure of 5mmHg.
（2）Pouring of polyurethane roller casting machine
① Technical key
The casting machine is the key equipment in the production of cast polyurethane elastomer (CPU), its main technical requirements are as follows
A.Precise proportioning and stable measurement: Adopt temperature and pressure resistant high precision metering pump and precision transmission, adjustment and display device, its measurement accuracy reaches 0.5%.
B.uniform mixing, no bubbles, the use of a special structure of high-speed mixing head, when the viscosity of the two components of the original liquid and the ratio is very different, but also to ensure uniform mixing, so that the production of products macro bubble-free, and flexible adjustment, easy to operate.
C.temperature stability, accuracy and reliability: temperature changes in the original liquid will affect the viscosity of the original liquid, pressure, metering accuracy and mixing ratio, so that the quality of products can not be stable. Especially the B component (MOCA) is solid at room temperature, if the material temperature is too low, it will die and can not be operated, the material temperature is too high, it is easy to change color and affect the quality of products. The circulating system of heat-conducting oil with electric heating is commonly used to heat the raw liquid, metering pump and pouring head, and the temperature is controlled by intelligent time-proportional digital display temperature control instrument.
② Pouring process: add MOCA (melting temperature >110℃) in B material tank, start the heating system of each component, make A and B material reach the required temperature and circulate each one, A material can be vacuum degassed first if needed to reach no bubble in prepolymer, make A and B material reach the required mixing ratio by adjusting the speed and displacement of metering pump according to the formula requirement. Start the pouring button, then A and B materials will be mixed evenly in the mixing cavity of the pouring head through high speed mixing, and when the discharged mixture does not contain bubbles in the transparent hose, it can be poured into the mold (the mold and roller core have been pretreated and preheated to 80-110℃). When the time between two pours is long (more than 1/2 of the life of the kettle), the mixing cavity needs to be cleaned automatically with cleaning agent (dichloromethane or trichloroethylene) (controlled automatically by computer programmer). When the pouring stops, A and B original liquid will automatically turn into their own circulation and return to their respective tanks.
(3) Polyurethane roller maturation and post-treatment
① Forming vulcanization (model vulcanization), polyurethane rubber roller vulcanization process in the mold before demoulding, its temperature can be selected as high as possible under the premise that its chemical structure is not destroyed, in order to speed up the chain expansion cross-linking reaction, shorten the demoulding time and improve the utilization rate of the mold and equipment, often at 100-200℃, 60-120min is appropriate.
② Post-vulcanization: refers to the process of continuing heating vulcanization of polyurethane rollers after demoulding, the temperature is slightly lower than molding vulcanization, 90-110℃, 3-10 hours is appropriate.
③ Surface reworking: Turning or grinding on the processing equipment according to the requirements.
Wuxi Coreco Material Technology Co., Ltd. is committed to developing new markets with excellent supply and service, satisfying customers, and showing competitive advantages in all aspects with loyalty and honesty. Our factory mainly produces and processes rolls for various surfaces, plasma spraying, ceramic coating and other processes.
