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Application of Low Shrinkage Epoxy Vinyl Resin in FRP Products

Jun 02, 2020

Low-shrinkage vinyl resin has better mechanical strength, rigidity, dimensional stability, heat cycle resistance and corrosion resistance than general-purpose unsaturated polyester, and it better meets high-quality FRP (fiber-reinforced plastic) Product requirements. The resin has been widely used in the development of FRP products in the automotive, train, kitchen and bathroom, shipbuilding, model, casting and other industries.

Vinyl resin is made by epoxy resin and methacrylic acid under the action of catalyst through ring-opening addition polymerization. It not only retains the basic segment of epoxy resin, but also has good process performance of unsaturated polyester resin. In addition, because it shows some special excellent properties after curing under suitable conditions, the resin has developed rapidly since the 1960s. first

As a category of unsaturated polyester resin, vinyl resin has higher activity and faster curing reaction speed, so that it has a larger curing shrinkage rate after curing. In order to reduce its cure shrinkage rate, many companies at home and abroad have been looking for technical solutions. Recently, Shanghai Fuchen Chemical Co., Ltd. has newly introduced an ultra-low shrinkage vinyl resin, which can fully meet their requirements after many users at home and abroad have tried it in batches.

About Ultra Low Shrinkage Vinyl Resin

The chemical name of the ultra-low shrinkage vinyl ester resin is bisphenol A epoxy vinyl resin, which is synthesized by the reaction of methacrylic acid and bisphenol A epoxy resin through a special catalyst, and is soluble in styrene solution. The mechanical properties of ultra-low shrinkage vinyl resin are shown in Table 1.

The resin has the following characteristics:

● Good toughness and ductility;

● Compared with ordinary vinyl resins (such as fumaric acid modified vinyl resins), this resin can not only improve glass fiber wettability to improve adhesion, but also withstand higher external impacts;

● With ultra-low curing linear shrinkage. According to the standard test method-"Determination of Linear Shrinkage of Epoxy Casting Resin" (HG/T 2625-94), the resin was tested, and the fumaric acid modified vinyl resin was selected for comparison. The test results are shown in the table 2.

Due to the unique properties of ultra-low shrinkage vinyl resin, such as sufficient mechanical strength, rigidity, dimensional stability, heat cycle resistance, and corrosion resistance, it can better meet the requirements of high-quality FRP (fiber-reinforced plastic) products. At present, the product has been widely used in the development of FRP products in the automotive, train, kitchen and bathroom, shipbuilding, model, casting and other industries.

Application of ultra-low shrinkage vinyl resin

1. FRP mould

In recent years, as the requirements for the performance of FRP products have become higher and higher, and the requirements for production efficiency and quality management have become stricter, the molds are required to have high performance and high functionality. At the same time, it is required that the core and the mold matching the mold cavity gradually expand to the form of low pressure (2~8kg/cm2) and heating (40℃~80℃). Therefore, for a pair of high-quality FRP molds, the following conditions must be met:

● Sufficient mechanical strength and rigidity;

● Sufficient dimensional stability;

● Sufficient heat resistance and heat cycle resistance;

● Excellent chemical resistance and wear resistance;

● Good flatness and gloss.

As a result, higher requirements have been placed on the materials selected for making FRP molds. The resin suitable for manufacturing molds must have the following characteristics:

● Low shrinkage characteristics, even reaching zero shrinkage;

● Good craftsmanship;

● After curing, it can provide sufficient mechanical strength and rigidity;

● Good heat resistance;

● Excellent corrosion resistance.

At present, neither o-benzene nor m-phenylene resin glass fiber reinforced plastic can satisfy the above-mentioned comprehensive performance well. The disadvantages of glass fiber reinforced plastic are:

● Poor heat resistance. The heat resistance of polyester fiberglass in the dry state is less than 80 ℃. When the mold is post-cured under circulating heating conditions, due to insufficient heat resistance, the mold is easily deformed, and the surface glass fiber is exposed, which affects the surface of the product. quality.

● Large shrinkage. Due to the internal stress of the curing shrinkage of the resin, the mold will generate micro-cracks and form surface defects, which will affect the strength and rigidity of the mold. Especially under the condition of alternating temperature or increasing temperature, the internal stress is released and the strength of the mold is reduced. In addition, shrinkage will also affect the dimensional accuracy of the FRP mold, and form traces of FRP fibers on the surface of the mold, thereby affecting the surface quality.

● Poor corrosion resistance. Mold release agent or mold release wax needs to be sprayed on the surface of the mold. These substances are basically organic and contain solvents. In addition, the resin in the mold will also produce styrene during the molding process, which will cause corrosion to the mold.

With the popularization and application of vinyl resin in the FRP industry, its excellent comprehensive performance has pushed the quality of FRP products to a new level. For a pair of molds, if the performance of the matrix resin on the surface of about 8mm is improved, its quality and service life will be qualitatively improved. Therefore, at present, many manufacturers at home and abroad will choose vinyl resin as the base material when making FRP molds, and their overall cost has not increased. See Table 3 for the production of FRP molds.

At present, the technical problems of vinyl resin curing shrinkage is one of the main problems that plague FRP engineers. Many FRP engineers use experience to determine the shrinkage margin when designing and manufacturing FRP products, and control the shrinkage by adding fillers and low shrinkage additives to ensure the dimensional accuracy of the products, but the actual effect is not obvious Will affect other performance.

The successful development and application of ultra-low shrinkage vinyl resin has brought FRP engineers a better choice. It can produce high-quality fiberglass molds and products, which has a profound impact on the FRP industry. The following is a brief introduction to the application of ultra-low shrinkage vinyl resin in the production of various types of glass steel molds.

(1) Vacuum plastic mold

In recent years, the vacuum blister molding process has developed rapidly. It is to fix the thermoplastic plastic sheet on the mold and heat it with a heater. When it is heated above the softening temperature of the sheet, the air between the plate and the glass steel mold is evacuated by a vacuum pump. With the help of atmospheric pressure, the The sheet is formed by covering the mold, and the part can be demolded after cooling. Whether the process can produce qualified products, the mold is crucial. Since the thermoforming temperature of plastics is generally greater than 100°C, and the heat resistance of ordinary polyester glass fiber reinforced plastics generally does not exceed 80°C in the dry state, the material for the mold should be selected with better heat resistance, strength and The resin material with better rigidity, and the ultra-low shrinkage vinyl ester resin not only meets the requirements of heat resistance, strength and rigidity, but also provides stable dimensional accuracy. Therefore, the resin has been well applied in vacuum blister forming molds such as bathroom and automobile parts.

(2) RTM mold

The RTM molding process is an important molding process in the FRP molding process. The requirements of the process for the mold are:

● Ensure the accuracy of product size, shape and matching accuracy of upper and lower molds, so that products can achieve A-level surface accuracy;

● With high enough strength and rigidity, it will not be damaged or deformed under the injection pressure of 50~150Kpa;

● It can withstand 10,000 times of thermal shock test of 85℃~120℃ when energized and heated without cracking or deformation;

● It has a long service life and can produce at least 3,000 products safely.

Generally, RTM molds include metal molds, FRP molds and so on. The advantages of FRP molds are low cost and short development cycle, but it also has deficiencies in dimensional accuracy, strength, rigidity, heat resistance, etc. These shortcomings have always limited the application of RTM FRP molds. With the introduction of ultra-low shrinkage vinyl resin, these problems have been effectively solved.

(3) Artificial marble injection mould

Because the artificial marble bath has a relatively high rigidity, when making a glass fiber reinforced plastic mold, special consideration should be given to the draft angle, and it is not allowed to cause reverse taper due to mold deformation, resulting in difficulty in demolding. For this reason, the artificial marble bath has higher requirements on the shrinkage, strength and rigidity of the mold material. Selecting ultra-low shrinkage vinyl resin as the material of FRP mold can meet this requirement well, and can use heating method (40℃~80℃) to shorten the production cycle and improve production efficiency.

(4) Hand lay-up and injection molding

In the FRP molding process, hand lay-up and spraying are the two most common main molding methods, and their molding molds are basically FRP molds. The glass fiber reinforced plastic mold made of ultra-low shrinkage vinyl resin has good dimensional accuracy, excellent surface quality and higher strength and rigidity, which not only extends the service life of the mold, but also improves the quality of the product.

2. Large area FRP sheet

At present, large-area FRP plates are widely used for their light weight, high strength, easy arrangement and designability. For example, they are widely used in physical and chemical plates in laboratories, countertop plates on vehicles, and medical equipment. Platform etc. These plates are required to have a high dimensional stability and high-strength mechanical properties after production, so as to be finally installed. Some general-purpose resins have large shrinkage, which causes FRP sheets to shrink, deform, or dent in the middle (uneven surface) after demolding, which brings a lot of inconvenience to installation, affects the appearance and final use. In addition, if it is used as a physical and chemical plate in the laboratory, the resin is required to have good acid and alkali resistance, and those conventional general-purpose unsaturated polyester resins do not meet the requirements for corrosion resistance. A large number of tests show that the ultra-low shrinkage vinyl resin has excellent corrosion resistance, as shown in Table 4. Therefore, the resin fully meets the requirements of the above products.

3. Polymer Concrete

Polymer concrete is made of polymer instead of cement as the bonding material, solidified and combined with aggregates and other fillers. At present, common artificial marble and integral resin mortar floors are polymer concrete forms. In the production of polymer concrete, the heat generated by the exothermic reaction after the pouring of the resin concrete causes the temperature of the concrete to rise. During the period when the exothermic reaction starts, the resin concrete is still in the stage from the flow state to the gel state. As a result, no shrinkage stress will occur. After reaching the exothermic peak, it starts to cool and harden and shrinks. The greater the shrinkage, the greater the tensile stress. Therefore, in the production of polymer concrete casting, the curing shrinkage of the resin is required to be small, and the exothermic peak is low. Otherwise, due to the large amount of heat generated by the curing of the resin, the resin will aggregate and cause the polymer concrete to crack. At the same time, the larger resin shrinkage will lead to greater internal stress inside the polymer concrete. Once the internal stress is released under high temperature or temperature alternation, the strength of the polymer concrete will be reduced. If the ultra-low shrinkage vinyl ester resin is selected as the matrix resin of polymer concrete, the above shortcomings can be well overcome.

At present, many artificial marbles are used in kitchen facilities or outdoor buildings. Because they are directly or indirectly exposed to open flames or sunlight, they place high demands on the weather resistance of the resin. As a methacrylic acid modified vinyl ester resin, compared with general unsaturated resin, it has better weather resistance and resistance to quenching and sudden heat, especially when used in kitchen countertops, due to the temperature around the stove Higher, will cause the artificial marble slab made of general-purpose resin to be heated and crack. However, vinyl ester resins have good heat resistance and can withstand high temperature thermal cycles.

4. Overall FRP production

At present, FRP materials have been widely used in the production of concept cars, parts and components and various models in the automotive industry. In these FRP products, not only the resin glass fiber reinforced plastic has precise dimensions, but also the base resin has high mechanical properties. As a high-performance special resin, vinyl ester resin has better mechanical properties than general unsaturated resin, thus greatly optimizing the application of FRP materials in the above fields.

5. Other applications

At present, the ultra-low shrinkage vinyl resin with its unique high performance has continuously expanded its application range, including bonding, marine products and so on. Due to the high toughness and good adhesion of the resin, it is particularly suitable for use as a corrosion-resistant lining of metal substrates such as carbon steel, which can better ensure the interface performance of the resin substrate and the metal substrate, thereby avoiding the stress or temperature difference Corrosion caused by the failure of the interface.