1, The performance of mold gel coat
The mold gel coat with superior performance can not only look at the strength, but also consider the heat resistance and mold release performance (including whether it is easy to demould itself, whether the product is easy to release after the mold is made), the surface gloss, the gloss retention rate, We have considered these problems in a comprehensive manner, and developed and produced a vinyl ester-type high-performance mold gel coat, which was compared with the physical properties of a general-purpose meta-benzene mold gel coat.
It can be clearly seen from the comparison that the vinyl ester type high-performance mold gel coat is superior to the general-purpose meta-benzene mold gel coat in all aspects.
2, The application of mold gel coat
The superior performance of the mold gel coat itself is on the one hand, and on the other hand, it is also very important. How to fully demonstrate the superior physical properties and play it out, the correct application is also the key. The operation of the mold gel coat is a crucial step in the mold making process. It can be said that the mold gel coat completely represents the entire mold, and all the back layup and structural skeleton are for the mold gel coat layer, high quality. The mold surface requires very precise mold gelcoat operation and application processes. The following is a brief description of the operation of the mold gel coat.
A, first determine the operation method, hand brush or spray, the viscosity, thixotropic index, etc. of the two have a certain difference, the viscosity of the gel coat of the hand brush is relatively high (about 4000mPa.s, 25 ° C), injection molding glue The coating viscosity is relatively low (about 2000 mPa.s, 25 ° C), but the thixotropic index of the spray molding is higher than that of the hand brush. In addition, there are certain differences in defoaming and leveling performance between the two;
B, the thickness of the mold gel coat is generally controlled to 0.6-0.8mm, uniform coating is required, the thickness is appropriate, it should be divided into two operations, and it is also divided into three operations (the first time is light color, it is easy to distinguish the grinding when grinding) ). The thickness is too thin to be worn, which does not function, and may cause under-curing. If the thickness is too thick, the toughness of the mold gel coat is lowered, and cracks such as cracks are easily generated when the force is applied;
C. The mold gel coat requires higher curing conditions than the general product gel coat. When spraying or hand brush construction, the gel time should be controlled well. It should not be too fast or too slow. Generally, it should be controlled at 40-60 minutes. It is possible to eliminate the possibility that the gel coat is cracked and pinhole bubbles are generated. The best performance of the mold gel coat can only be fully realized after it is fully cured. Therefore, after the whole mold is finished, it must have a post-cure process to ensure that the superior performance of the mold gel coat can be fully reflected.
3. Post-laying and treatment of the mold
After the mold gel coat is hand-brushed or sprayed, the next step is the paste of the reinforcement layer. In order to ensure the performance of the mold gel coat and fully exerted, there should be several places in the processing after the paste reinforcement layer and the mold is finished. There are a few points to note. Because the mold gel coat and the back layup are complementary, the back layup serves the mold coat layer.
A. Use of transition layer surface felt
The role of the surface felt: a enhance the gel coat layer to prevent the formation of microcracks; b for the appearance of the surface of the gel coat layer, to avoid the transmission of the cloth and bundle wires to the gel coat surface, to ensure the smoothness of the surface; c to form a layer of resin Layer to improve cohesion and impact resistance between gel coat and laminate. After the surface felt is laid, when it is impregnated with the resin, the resin is slowly pressed with a brush to prevent the surface felt from moving to cause air bubbles. It is also preferred to use a tough resin to form a transition layer between the mold gel coat and the reinforcement layer. In addition, the surface felt layer should be cured separately, and after curing, the air bubbles trapped therein are carefully excluded.
B, The reinforcement of the reinforcement layer
The thickness of the FRP mold is generally 2-3 times of the thickness of the product. During the paste process, it should be formed in multiple times to avoid the opening of the heat peak and reduce the shrinkage rate. Generally speaking, the more the number of times, the smaller the shrinkage rate. At the same time, the fiber should pay attention to the combination of the felt cloth, and the use of the felt, the thickness of the felt increases rapidly, and the strength of the cloth is high. If reinforcing ribs are required, the shape of the ribs must conform to the contour shape. The purpose of the ribs is to transmit the external force to the surface of the mold on average to prevent deformation of the surface of the mold. The most basic cause of cracking in the mold gel coat is the deformation of the mold. Because of this, designing a rigid mold structure will greatly prevent cracking of the gel coat. When the reinforced layer is pasted, special mold resin should be used. Whether the mold is deformed depends mainly on the shrinkage of the mold resin used. If a resin with a small cure shrinkage is selected and slowly solidified, then it is completely cured, which is a texture. An important factor in good FRP molds. The selection principle of the mold resin: small curing shrinkage, toughness, suitable operation viscosity, good heat resistance and sufficient strength, currently used more is an isophthalic resin or a modified vinyl ester resin.
C, Processing of FRP mold
After the mold is finished, it should be placed at room temperature for about two weeks. In order to ensure the complete curing of the mold gel coat and resin, it is better to have a post-cure treatment to make the strength and rigidity of the mold gel coat and resin. Get the best. After the parting, a very important point is to polish, do not use very thick sandpaper when starting a good mold, it should start from 800 mesh or even 1000 mesh water sandpaper, so as not to damage the gel coat layer, every time sanding the sandpaper Rinse with water to remove the coarse sand left on the sandpaper. After grinding in place, the surface of the mold can be polished. The polishing agent must be thick and thin, first hard and then soft. The main factor affecting the surface glossiness of FRP products is the surface gloss of the molding die. Therefore, the mold itself must be polished to achieve the surface gloss of the “mirror effect”.
D, The use of new molds
When the new FRP mold is put into use, there is often a sticking phenomenon, which causes damage to the mold gel coat. In severe cases, the mold may be scrapped. Therefore, when the new mold is put into use, it must be ensured that the release agent is evenly applied. Then, when making the first to third products, the water-soluble release agent can be applied once every time, so that the mold and the mold can be protected. The product is easy to release and easy to clean. A mold can not be used once and for all, must be used while maintaining, and after the use of a paragraph behind, pay attention to storage, to prevent accelerated aging of the mold gel coat, so as to ensure that the number of repeated use, the life of the mold can be extended.
4, The conclusion
In order to produce a product with beautiful appearance and reasonable structure, the first condition is to have a high-quality mold that has been carefully designed and manufactured, meets the requirements of product drawings, has a high appearance and smooth surface, and is the first to bear the brunt of the choice of mold gel coat. And application. The vinyl ester type high performance mold gel coat introduced in this paper has the characteristics of high hardness, heat resistance, wear resistance, good polishability, high brightness and long service life, as long as the correct operation and use, and in the mold after the production and Attention can be paid to the treatment, and the superior performance of the mold gel coat can be fully realized to produce high quality FRP products. At present, vinyl ester-type high-performance mold gel coats have good applications in shipbuilding, rail transit, helmets and other sports equipment molds.