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Resin Heavy-duty Vinyl Ester Resin Curing System

Jun 17, 2020

Guiding formula for vinyl ester resin on-site construction and curing

1 Preparation of resin compound

A resin compound containing cobalt naphthenate and dimethylaniline (if necessary), it is more appropriate to mix 20~250kg at a time. The compound contains accelerators and co-accelerators, but no curing agent. Generally, it is prepared. If appropriate, the compound can be stored for several weeks. The resin compound should be prepared by a specially designated, reliable technician, and carefully prepared, and the curing characteristics and uniformity of the compound should be reviewed from time to time. The resin compound can ensure that the amount of accelerator and co-accelerator is uniform every time it is used, it can give the operator a curve of the change of the gel time and operable time of a single curing agent, and it also helps to compensate for the temperature and other The impact of changes in environmental conditions. For the preparation of the rubber compound, it is necessary to thoroughly mix the accelerator, dimethylaniline and resin, and a high-speed pneumatic agitator is a good tool.

Appropriate safety protection is necessary. Protective glasses and protective clothing should be worn when touching resins, accelerators, co-accelerators and curing agents. Good housekeeping measures should be followed in the work area to minimize pollution. Proper ventilation should be maintained, and disposable containers should be used when mixing. Used containers and resin waste should be disposed of properly and disposed of in accordance with relevant laws and regulations. For each batch, the operator may add different amounts of MEKP (within the specified range) to obtain the required gel time (typical gel time is 25~30min). MEKP should be weighed carefully and accurately, and thoroughly mixed with the resin, stirring for at least 30 seconds, the stirring needs to reach the place including both sides and bottom of the container. The operator should try to avoid or reduce the bubbles brought into it when mixing.

The following are the several steps of resin compound preparation:

(1) Take the resin material temperature and the ambient temperature into consideration, and estimate the required operation time. When considering the operation time, it is necessary to consider the resin viscosity (affected by the temperature) and the difficulty of operation.

(2) If the on-site mixing method is adopted, such as pure resin plus thixotropic agent, accelerator, high-speed shearing and stirring to achieve the expected thixotropic index, then a certain amount of heat will be generated due to high-speed shearing, so try to operate Do shear mixing before use, or thixotropic before adding accelerator.

(3) The accelerator/curing agent addition table can be used as a reference to the data given by the supplier, and the appropriate addition ratio can be selected to achieve the desired operation time.

(4) Weigh the resin, accelerator, curing agent, dimethylaniline, and if necessary, weigh the polymerization inhibitor (dissolved in styrene or other suitable solvent in advance), and place it separately. The conversion of volume and weight can refer to the appendix, which is helpful for the direct measurement of the measuring cup during actual operation.

(5) Add the cobalt accelerator solution to the resin, mix thoroughly with a starter mixer, pay attention not to be too fast when mixing, and not too shallow to avoid excessive air bubbles during mixing.

(6) Add DMA or DEA and mix evenly.

(7) Add other additives such as polymerization inhibitors and mix evenly.

(8) Add pigments, color pastes, fillers (such as aluminum hydroxide, antimony oxide), etc., and mix evenly.

(9) After all the ingredients have been added, thoroughly stir and mix again.

(10) Add the prepared accelerator and filler in advance to a small amount of resin, and test the gel time of the test sample. You can refer to the recommended data provided by the supplier.

(11) The polymerization inhibitor can extend the gel time, dimethylaniline can shorten the gel time of the blue and white water curing system, the amount of polymerization inhibitor and dimethylaniline added to the resin is very small, Adding more will result in no gel or gel too fast.

(12) Prepare the resin compound with curing.

(13) If the resin exotherm is too high, some copper naphthenate or a-methylstyrene can be added appropriately. A little addition of copper naphthenate will not have much effect on the gel time when using standard MEKP. If the addition amount of copper naphthenate or polymerization inhibitor exceeds 0.04%, the curing degree of the resin will be affected.

2 Influencing factors of gel curing

The quantity of curing agent, accelerator and co-accelerator is very small compared to resin, and it needs to be particularly accurate when weighing. Equipment such as discarded syringes, graduated plastic measuring cylinders, plastic measuring cups, etc. can be used. The gel time of the actual resin will be greatly changed due to the minor changes of these auxiliary materials. In addition, a small amount of reactants are weighed, the difference between batches of resin, the environmental temperature, the environmental humidity, the thickness of the FRP, The type of mold etc. have an effect on the gel time.

3 Weighing

For the measurement of trace chemicals, use a graduated scale as much as possible. Such as syringes, measuring cups, measuring cylinders, balances. Be sure to reduce the weighing error of auxiliary materials such as accelerators, curing agents, and mold release agents.

Weighing must be accurate in the small test, and the temperature control of the test must also be recorded. After the small test, the curing characteristic data in the disposable cup is not enough to explain all the problems. Sometimes it is necessary to imitate the actual molding for fiber stacking. Operate on a certain substrate to verify the gel time on the actual mold.

4 Small sample

Samples of small materials are generally prepared in disposable cups or plastic scoops. After mixing, the small sample stacking test is performed on the actual mold. Confirm the operation time, gel time, heat release, fiber wettability, operation processability and other issues that need to be considered in advance for large-scale production.

5 Gel time and temperature

The epoxy vinyl ester resin is polymerized and cured using a radical curing initiator. There are many factors in the resin curing process, so its catalytic system needs to change accordingly. The selection criteria of the catalytic system follow the following principles: (1) expected gel time; (2) operating temperature; (3) heat dissipation effect of mold or substrate; (4) post-curing effect; (5) product thickness and shape.

For the effect of different ambient temperatures on the gel time of vinyl ester resins, please refer to the single-page technical description materials for specific brands.

When unsaturated polyester resin and vinyl ester resin are used in operation, the amount of accelerator and curing agent added is very important. You can find some of your desired addition ratio data in the TDS of specific products, such as different temperatures to obtain the desired Proportion of accelerator curing agent added during operation time. Although these are very specific and detailed, it can only be used as a reference for you, and cannot be regarded as a specification value. There are many factors that affect the setting time. Without affecting the gel time, one of the most effective ways to control the exotherm is to add 0.04% copper naphthenate. If the standard MEKP is changed to a peroxide curing agent with low hydrogen peroxide content (BPO, CHP, non-foaming MEKP), the gel time will be greatly changed, and you should pay attention to this point when using it.

The data in the data is laboratory data. In actual operation, it can only serve as a reference. The amount of accelerator curing agent added should be based on actual environmental temperature, environmental humidity, resin temperature, substrate temperature, FRP thickness, etc. Adjust accordingly. High temperature will cause the resin gel to speed up. In addition to the normal operating environment temperature, there are some hidden "high temperatures", such as high temperature of the resin material, direct sunlight, near the heat source, and too thick the product, which will cause the resin to gel The glue time is shortened. Low temperature will cause the resin gel to delay. In addition to the normal low ambient temperature, there are some hidden "low temperatures", such as low resin temperature, low substrate temperature, low mold temperature, too thin products, and too much filler fiber content. Higher will lead to longer resin gel time. When the gel time is too short to operate, you need to adjust the amount of accelerator added, or you can adjust the accelerator curing agent together.