The curing of resin– unsaturated polyester resin (UPR) and vinyl ester resin (VER) involves a recognized mechanism of free-radical curing, which is categorized into stages of initiation, propagation, termination, and also involves chain transfer. Curing methods include heat, light, electron beam, ultrasound, etc. However, in current applications of UPR and VER in fields such as fiberglass, resin-heavy corrosion protection, coatings, and structural adhesives, the predominant method remains initiator-induced curing, while in some cases, photopolymerization is also utilized.
The curing mechanism using peroxide as initiator seems to have been thoroughly studied in theory and practice, but in actual applications, this is not the case. A large number of customers are interested in unsaturated polyester resin (UPR) and vinyl ester resin. The curing control of (VER) is inconclusive. It is believed that the curing control of this type of resin is very “squeamish”, “adding too much is too late, adding too little will not cure”. Experts of Thousands Chemicals believe that the essential reason for this phenomenon is that there are too many and complex factors that affect the free radical curing of resin （UPR and VER）, and the downstream applications are diverse, including thin, thick, room temperature curing, and medium and high temperature curing. The specific situations vary greatly. If unsaturated polyester resin (UPR) and vinyl ester resin (VER) cannot be cured well, or “properly cured”, then the final composite materials, coatings, resin heavy anti-corrosion, structural adhesives, etc. will have quality problems. The likelihood of defects and blemishes is greatly increased.
In view of this, Experts of Thousands Chemicals believe that it is indeed necessary to deeply explore the curing and molding defects of UPR and VER to provide more accurate and in-place services to all customers and friends.
The external performance of the curing process of unsaturated polyester resin (UPR) and vinyl ester resin (VER) is divided into three stages, namely:
1. Gel stage: counting from the time after adding the curing agent and accelerator until the resin solidifies into a jelly and loses fluidity. In this section, the resin can melt and be soluble in certain solvents (such as ethanol, acetone, etc.). This stage takes about a few minutes to tens of minutes.
2. Hardening stage: starting from the time when the resin gels until it becomes hard enough to be basically non-sticky. In this stage, the resin can swell but not dissolve when in contact with certain solvents (such as ethanol, acetone, etc.), and can soften but not completely melt when heated. This stage takes approximately tens of minutes to several hours.
3. Aging stage: After being placed at room temperature, counting from the time of hardening, it reaches the required hardness of the product and has stable physical and chemical properties for use. During this stage, the resin neither dissolves nor melts. What we usually refer to as post-curing refers to this stage. This stage is usually a long process. It usually takes several days or weeks or even longer.
During the free radical addition polymerization reaction of unsaturated polyester resin (UPR) and vinyl ester resin (VER), the monomer styrene slowly decreases, the conversion rate increases, and the degree of curing increases. However, theoretically, styrene does not May be fully 100% cured, even with post-heat treatment, trace amounts of styrene monomer may remain.
The free radical addition polymerization reaction of unsaturated polyester resin (UPR) and vinyl ester resin (VER) is an exothermic reaction, and the release of heat in turn accelerates the free radical addition polymerization reaction. Therefore, the effective control of the curing heat release process of unsaturated polyester resin (UPR) and vinyl ester resin (VER) is a problem that different customers need to face. The proper control of the heat release amount and heat release speed is the key to Necessary conditions for curing of resin.