The manufacturing process of unsaturated polyester resin (UPR) involves several steps, including the preparation of the raw materials, reaction and polymerization, and post-processing. Here is a general overview of the UPR manufacturing process:
Raw Material Preparation:
Unsaturated Dicarboxylic Acid/Anhydride: The first step involves selecting the appropriate unsaturated dicarboxylic acid or anhydride, such as maleic anhydride, phthalic anhydride, or fumaric acid. These acids or anhydrides provide the backbone structure for the polyester resin.
Diol: A diol, usually propylene glycol or ethylene glycol, is chosen as the second raw material. The diol introduces the reactive hydroxyl (OH) groups into the resin, which will later react with the unsaturated double bonds during polymerization.
Initiator: A peroxide-based initiator, such as methyl ethyl ketone peroxide (MEKP), is used to initiate the polymerization reaction.
Reaction and Polymerization:
Esterification: The unsaturated dicarboxylic acid/anhydride and diol are mixed together in a reactor. A catalyst, typically an acidic compound like p-toluenesulfonic acid, is added to facilitate the esterification reaction. This reaction results in the formation of an unsaturated polyester pre-polymer, which has hydroxyl groups and unsaturated double bonds along its chain.
Chain Extension: To further increase the molecular weight and improve the properties of the resin, a chain extender, such as glycol or glycerol, may be added to the reaction mixture. This step involves extending the polyester chains by reacting the hydroxyl groups of the chain extender with the remaining unsaturated sites on the prepolymer.
Catalyst Addition: Once the desired molecular weight is achieved, the peroxide-based initiator (e.g., MEKP) is added to the mixture to initiate the cross-linking reaction.
Post-Processing:
Bulk or Solution Polymerization: The reaction mixture can be subjected to bulk polymerization, where it is heated to a specific temperature to facilitate the curing process. Alternatively, it can be dissolved in a suitable solvent, such as styrene, and undergo solution polymerization. In the case of solution polymerization, the solvent helps reduce the viscosity of the resin and aids in its application.
Deaeration: The resin mixture is typically deaerated to remove any trapped air or bubbles that may affect the quality of the final product. This is achieved by subjecting the mixture to vacuum conditions and allowing the air to escape.
Packaging: The fully cured and post-processed UPR is usually packaged into containers or drums for storage and transportation.
It’s important to note that the exact manufacturing process can vary depending on the specific formulation, desired properties, and intended application of the unsaturated polyester resin. Manufacturers may also incorporate additives, pigments, fillers, or other modifiers to tailor the resin’s characteristics to meet specific requirements.
