Currently, many countries have strict regulations on the legal standards for the production of styrene in the environment, for example, the United Kingdom 100ppm; France 50ppm; Germany 20ppm; Sweden 20ppm; Norway 25ppm; Holland 50ppm.

Therefore, it has become an important topic in the FRP industry to find a way to reduce the volatile amount of styrene.

Closed-mode technology is an effective method to reduce the volatile amount of styrene. This article will be devoted to several aspects of closed-mode technology.

Glass fiber reinforced plastic closed mold technology, refers to the injection of resin into the closed mold, without exposure to external air conditions, the completion of the curing process of process.

Closed-mode technology has the following types: Vacuum injection, resin transfer molding (RTM), Structural Reaction Injection Molding (SRIM), injection process, enhanced Reaction Injection Molding (RRIM), etc.

For vacuum injection, RTM, SRIM, and other three kinds of closed-mode technology, equipment investment to SRIM the highest, followed by RTM, the lowest vacuum injection.

These process methods, in the processing cycle, automation level, batch size, and so on, there is a certain regularity.

For example, the processing cycle for the shortest SRIM (about 8 minutes), RTM second (10-80 minutes or so), vacuum injection Molding the longest (1 hour to more than 10 hours). The level of automation, with SRIM as the highest, its annual production capacity is also highest, production costs included the lowest labor costs.

These processes are using the resin injection method, an important difference is that the reinforcement material, is in the closed mold before, or resin impregnation before, put into the mold.

This is a very important factor for the control of the content and directional arrangement of the enhanced materials RTM and SRIM process, which is beneficial to the control of glass fiber content due to the use of the technology.

It must be pointed out that when using closed-mode technology, the resin used is also very important. Vacuum injection resins, low shrinkage RTM resins, and mixed resins are usually used.

Vacuum injection Molding Process
The process uses resin injection technology and is supplemented by a vacuum to facilitate the injection process. Usually, there is a deformable membrane to be used as the other side of the mold. Half of the mold generally can be used hand lay-up mold or injection molding mold, only a little modification can be used.

This process does not require a large number of tooling or equipment investments, the production of large quantities of products of higher quality.

The reinforced material used in the vacuum injection molding process can be chopped fiberglass mats or Kevlar or carbon fiber fabrics.

The advantages of the process are as follows: No styrene volatiles, clean working site, easy bonding of core and inserting parts, low investment in equipment, hand lay-up, or injection moulds.

However, the vacuum injection molding process is also deficient, such as the vacuum injection process must be used as reinforcement material, the price is slightly more expensive than roving, and such as, felt material and film positioning is more difficult, compared with the injection molding, and so on.

Vacuum injection Molding process made of products, mainly used in boats, transportation, construction, and other aspects.

For example, can manufacture all kinds of FRP Truck body sandwich plate and bus integral sandwich board, Windmill fan Peng (11m long, glass fiber content is 68%), offshore oil platform sandwich board, building roof, and so on. Vacuum injection Molding process, suitable for manufacturing batch medium, mechanical performance requirements Medium or High, 2 meters above large parts.

The process can be considered as a resin injection process under low pressure, with stress of about 0.3~0.6MPa. In recent years, many RTM resins have been developed and the high-quality A-level surface can be obtained.

These resin systems, with low shrinkage additive, have an optimum curing temperature of about 70 ℃, far below the curing temperature of the 140~160℃ of the normally SMC low shrinkage system.

At present, the majority of the RTM process uses plastic resin, to obtain a better surface quality. However, when using a low shrinkage RTM system, it is not necessary to use the adhesive resin, which will not produce styrene volatiles.

The development market for RTM products are mainly in the automotive and construction industries, as well as other areas requiring higher surface quality. At present, the main research and development and establishment of RTM machine systems abroad

Includes A-class surface quality RTM resin, high-temperature RTM process parameters, injection equipment evaluation.

Belgium’s largest FRP production Enterprise Indupol Company, successfully developed the RTM resin and its corresponding process technology, not only to ensure product reproducibility but also to reduce work hours.

DSM resins developed mixed resins of unsaturated polyester and polyurethane, its performance can be achieved: viscosity is lower than 200~400mpa. s (at room temperature), fast curing speed at low temperature (70 ℃ gel time is 1 minutes), higher mechanical strength and modulus, fracture elongation rate is ±7%.

Structural Reaction Injection Molding process (SRIM)
The process molding equipment should include the following parts: reinforced material pre-forming machine, production tooling, jig, and injection machine. In industrial production, SRIM often needs to support a reinforced material pre-forming machine, the preformed period of about a few minutes.

There are usually two kinds of pre-forming methods, one is continuous short cut felt hot forming method, with infrared heating felt piece, plus binder hot-pressing solidification pre-molding;

The other is the direct injection of glass fiber method, using chopped fiber and mixed with a small amount of powdered binder spray, and suction adsorption to sieve screen, then melt pre-forming solidification cooling.

Today’s remote control technology allows the fiber to be placed exactly where it is needed. For some products, such as tablets, you can not need the pre-forming process, also often can not be onlineSRIM pre-forming, by the partner according to the shape of the product, to complete the pre-forming process.

SRIM molds can be made from different materials. Usually SRIM process of the annual volume, up to thousands of pieces, so often used nickel mold, can also use an aluminum mold or alloy mold. These non-steel molds, not only the pressure and temperature can be reduced and can save more mold costs.

Generally speaking, the closed-mode effect of SRIM is more rigorous, the pressure range is wide, the injection pressure is low, the average value is about 1MPa.

The injection machine usually has two premixes, generally, in the non-critical state mixed resin, the blending ratio is wide. The blending resin is injected into the heating mold after the premix.

Injection machine price, between the jet molding machine and PU mixer.

The characteristics of SRIM process are as follows: No styrene volatile quantity, good product quality, both sides bright, no fiber exposure; the content and location of the enhanced material in the product is more accurate

Thus its strength is higher and the equipment investment is low. Its product development of the main market, is the transport, construction of electrical and electronic industries.