What factors affect the gel time of unsaturated polyester resin?

Unsaturated polyester resin.

The curing is an exothermic reaction that can be divided into three stages:

Gelling stage: The time from the addition of accelerator to the time when the unsaturated polyester resin becomes a gel state, is.

The most important stage of the curing process.

Factors affecting gelling time: polymerization inhibitors, initiators.

and the amount of accelerator added, crosslinker.

evaporation loss, ambient temperature and humidity, etc.

Hardening stage: The time from the time when the resin begins to gel until it has a certain hardness and can be removed from the mold.

Full curing stage: Usually at room temperature, it can take a few days to a few weeks.

Gelling time, also known as gelling time. Generally, it refers to the time it takes for a liquid resin or glue to transform from a liquid state that can flow to a solid gel at a specified temperature. For thermosetting resins, it refers to the time required to form a gel after adding accelerators and initiators at a certain temperature (usually 25 °).

So what conditions affect gel time based on our daily operations?

The main influencing factors are: temperature, humidity, accelerator initiator dosage, and accumulation thickness.

The two most fundamental conditions are temperature and the amount of accelerator initiator.

The higher the temperature, the faster the reaction and the shorter the gelling time. The lower the temperature, the longer the gel time.

Adjusting the ratio of accelerator to initiator additions also makes it very intuitive to control the gelation time of unsaturated polyester resins. Within a certain range, the larger the addition ratio, the shorter the gel time, and vice versa. (But the ratio of excess accelerator to initiator has no effect on gel time).

In fact, when we do FRP, no matter which process, the gel time is mainly controlled by adjusting these two parameters.

The gelling and curing of unsaturated polyester resins is essentially a process of polyaddition. The polyester macromolecular segments in the resin contain C=C double bonds (non-aromatic), and the crosslinker styrene also contains C=C double bonds (non-aromatic), and they can undergo polyaddition reactions both on their own and with each other. After the c=c double bond is broken, it is cross-linked into a network polymer, thus forming a complex three-dimensional cross-linking structure.

The c=c double bond cleavage to form a free radical requires an initiation condition, and the temperature and initiator do this job, so the speed of the polymerization reaction can be controlled mainly by these two conditions. (Guangdong Bohao Composite Materials is a composite materials industry overall solution service provider, committed to providing customers with more complete composite product solutions, more top composite materials technology and technical services, more advanced composite material mold design and manufacturing.) The solution comes from Bohao!

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Good morning, whether it is or equal to aromatic unsaturated polyester, there are three components, namely polyester monomer, catalyst and crosslinker, there is a linear correlation between them, and the curing process can only be completed after the gel is reached and then the initiation density is reached - the viscosity will also rise sharply after reaching the crosslinking threshold, and the curing time is uncontrollable. Does not affect the gel time My understanding is that the gel time is the same as before, but the curing rate in the second half is significantly accelerated, that is, you can use modified or latent curing agent to complete this step, after all, the aromatic ring is not opened, it is not opened, it is not opened, it is not opened, and the game function of pressing the pause button to stand still is not opened, and the exothermic coefficient of the overall curing interval is best to be gentle, I was interested in trying this modified polyester before, and the initial setting was 6 hours and 30 minutes after the end - the finished product was miserable. Rapid curing leads to a serious decline in the properties of polyester and turns into glass slag (dielectric strength, impact notch, hardness and cross-linking density, etc. are extremely poor). You can also consider using latent peroxide or mixed cross-linking agent, using the free radicals released by the former such as MEKP and DCP or heat to reach the threshold and then trigger a strong cross-linking, or the initial setting in the first half is the opposite to play a role in inhibiting polymerization, and the antipolymerization components and other additives in the unsaturated resin cancel each other out and enter the curing process (hard blocking the curing agent does not let it cross-link with the monomer to delay time).

In short, it is two suggested ideas, and I don't know if I can help you, my personal superficial understanding is to focus on the improvement of curing agents, please refer to it as appropriate.

It should be shortened gel time. Generally speaking, it depends on the thickness of the product. If he said above, it is enough to add more accelerators to speed up the gel time.

If it is a thick product, the ratio of accelerator and curing agent should be 2:1, and generally the product should be 1:1 at room temperature.

At present, the quality of curing agents and accelerators used in Shandong is relatively chaotic, some curing agents have a pH value of less than 3, high acidity, and some curing agents have high water content, measure its density in a few, and some accelerators use some toxic solvents, such as methanol, etc., so we hope that we should choose the best curing agent and accelerator, which is the basic guarantee for FRP products. For example, Tianjin Aksu, Zhejiang Huangyan, Jiangyin Qianjian, Changzhou Tianpeng, Shanghai Changfeng, Shanghai Shengfei and other enterprises should be our first choice. In the current summer, the curing agent of some FRP products needs to be used to 4%, which is incomprehensible, so how much water is brought into the FRP?

1. The dilution is too fast, and the temperature of the dilution kettle is too high, and the dilution is generally controlled at 60-90 degrees.

2. Whether the amount of polymerization inhibitor is appropriate, the resin temperature is high when the resin of the reactor is diluted to the dilution kettle, so the polymerization inhibitor should be able to control the polymerization of the high-temperature resin when it enters the dilution kettle.

1. The molecular weight is controlled by acid number in the production process.

2. The phase separation is controlled by the amount of styrene added during the dilution process.

3. The choice of curing agent, moisture content will directly affect the degree of curing.

4. The temperature during curing will affect the degree of cross-linking of molecules.

Unsaturated polyester resin is prepared by the reaction of diols or polyols with phthalic anhydride and maleic anhydride, and the titration acid number can only determine the end point of the reaction, and the size of the molecular weight is determined by the type of raw materials, such as ethylene glycol and propylene glycol are produced by different molecular weights, and other alcohols are produced differently.

A The curing process of epoxy material is a very complex process of physical and chemical change, and there are many influencing factors. The curing process and influencing factors of epoxy resin can be summarized as follows.

1. Wetting and impregnation of solid materials (fibers, fillers, bonded surfaces, coating substrates, etc.) by epoxy adhesive solution (liquid epoxy resin glue, or epoxy resin solution, or epoxy resin melt). It can also be made into prepregs or molding compounds. The main influencing factors are the compatibility of the glue with the solid material (affinity, which can be improved by adjusting the glue formulation design and solid surface treatment, etc.) and the viscosity of the glue (depending on the glue formulation and ambient temperature).

2. The material fills the mold cavity or leveling to form a dense object. The main influencing factor is the fluidity of the material, mainly the viscosity of the glue. It all depends on the glue formulation and the ambient temperature. Pressurization and vacuuming can be used to assist in mold filling and the formation of dense objects.

3. Carry out the curing reaction. Under certain conditions, epoxy oligomers begin to react with curing agents and modifiers, and solidify three-dimensional cross-linked structures from glue gelation to vitrification. The main influencing factor is the thermal history of the system.

Including: preheating temperature, ramp-up rate, curing temperature, curing time, post-curing temperature and time, etc. In addition, the curing pressure also plays a certain role in the curing reaction and the compactness and shape stability of the product.

The main influencing factors are glue formulation and ambient temperature and humidity.

Fourth, the structure formation of epoxy matrix (epoxy cure). This is formed gradually as the curing reaction of the epoxy resin progresses. It includes the formation of the chemical structure of the solidified matter and the formation of the aggregate structure of the solidified matter. The main influencing factor is the thermal history of the glue formulation and system.

5. The formation of the interface layer structure of epoxy materials. It is also gradually formed as the curing reaction of epoxy resin progresses. It depends not only on the glue formulation and the thermal history of the system, but also on the surface properties of materials such as fibers and fillers.

To sum up, the main factors affecting the curing process of epoxy materials are the glue formula and the surface properties of solid materials such as fibers and fillers, which depend on the correctness of the material design; - Thermal history and pressurization process, such as the amount of pressure, the timing of pressurization, the number of pressurization, etc., depends on the correctness of the process design, which is commonly referred to as the three elements of the molding process: temperature, time, and pressure.