The FRP continuous plate forming process is a process in which unsaturated polyester resin is impregnated with glass fibers on a continuous forming machine, and then heated and solidified by a template to obtain a continuous plate with a specific cross-sectional shape. Compared with other materials, FRP sheet has the characteristics of light weight, high strength, and good impact resistance, especially its unique light transmittance (the light transmittance of 1.2mm thick FRP light transmittance plate can reach 90%) and cross-section designability. In addition, FRP boards also have excellent corrosion resistance, weather resistance and color arbitrariness, so they are widely used in greenhouses, solar water heater covers, industrial plants, warehouses and other aspects of lighting, anti-corrosion and decoration.
In the 1980s, the production process of FRP sheets was mainly hand lay-up, with low production efficiency, unstable quality, uneven cross-section thickness, surface wrinkles, and many bubbles. It was mainly used in bicycle sheds and market sheds. In the 1960s, the United States successfully developed FRP sheet continuous forming technology and production equipment. my country began to introduce this equipment in 1985. In the early 1990s, self-developed production lines came out. into production. Since 2002, the localization of equipment has been promoted on a large scale.
Reinforcement material
The reinforcement materials usually used for FRP panels are non-alkali glass fiber cloth, untwisted glass roving, and non-alkali glass fiber mat. In the early 1990s, glass cloth was used in the continuous production of corrugated boards. The strength of the produced boards was relatively high, but the appearance was not good (especially in the application of light-transmitting boards), the process control was difficult, and the yield was low. In the late 1990s, is no longer selected. At present, manufacturers choose glass fiber chopped strand mat or chopped twisted glass yarn according to their own units.
1. Glass fiber chopped strand mat
At present, the specifications of chopped strand mats commonly used in China are divided into EMC300, EMC450, EMC600, etc. according to thickness (gram weight). Because EMC600 has obvious lap joints during use, it affects the appearance and is prone to waste products. It is rarely used now. According to the use width, there are 540mm, 1040mm, 1270mm and so on. Chopped glass fiber mat is a sheet made of continuous long fibers cut into 50mm short fibers by a cutting roller, evenly scattered into a thin layer, and then made of a binder (usually powder). Requirements: Uniform dispersion of fibers, good wettability, refractive index as close as possible to resin, etc. Refer to the table below for general indicators of commonly used fiber mats.
Performance Index of Glass Chopped Strand Mat
Specification EMC300-1040/EMC450-1040
Moisture content %: GB/T 9914.1-2001 idt ISO 3344: 1997 ≤0.20
Combustible content %: GB/T 9914.2-2001 eqv ISO 1887: 1995 1.8~8.5
Mass per unit area g/m2: GB/T 9914.3-2001 idt ISO 3374: 2000 300±30/450±45
Mass variation coefficient per unit area: GB/T 9914.3-2001 idt ISO 3374: 2000 ≤6.0
Styrene solubility s: GB/T 6006.1-2001 eqv ISO 2558: 2000 ≤40
Soaking rate s: GB/T 17470 Appendix A <100
Tensile breaking strength (transverse/longitudinal) N: GB/T 6006.2-2001 idt ISO 3342: 1995 ≥60
Note: Refer to the provisions of GB/T 17470-2007 for appearance quality
2. Chopped untwisted glass roving
The untwisted glass rovings used in the continuous FRP sheet forming process should have good dispersion, uniform spraying, good resin wettability, and a refractive index close to the resin. Because the cost is relatively low, it has been used by more manufacturers since 2006.
Among the first three foreign production lines introduced, two were produced in the UK and one in the United States. The design concept of British system equipment is to use glass fiber chopped strand mat, and the design concept of American system equipment is to use chopped strand yarn. The difference is that the equipment using yarn needs to reach 30% glass fiber content, and it is easy to pile up yarn at the thickness control roller of the equipment, which needs to be solved by adding polyester yarn along the direction of the equipment. In 2004, a production line for FRP boards, which is said to be produced in Australia, appeared. Chopped yarns were used without polyester threads, but the glass fiber content was only about 22%. The appearance of the boards was not bad, but the strength was low.
Resin matrix
At present, most of the continuous FRP sheet forming processes use o-phthalic or isophthalic unsaturated polyester resin (UP) resin, and some products with special requirements use vinyl resin (mostly opaque and corrosion-resistant sheets). Ortho-phthalic resin can meet the normal use in general occasions, with high strength and good weather resistance; there is no difference in the performance of the board produced by iso-phthalic resin, but the aging and attenuation speed of iso-phthalic board is faster than that of ortho-phthalic board. much slower.
In terms of parameter selection, the resin should have low shrinkage and appropriate viscosity so that it can impregnate glass fibers well. For lighting panels, the resin must have excellent light transmission after curing, and the refractive index of the resin casting body should match or be basically the same as that of the glass fiber. Because FRP boards are mostly used outdoors, especially transparent boards, UV absorbers (such as UV-9, UV-531, etc., but expensive) must be added to the resin.
The characteristics of the resin used for continuous FRP sheets are as follows (due to the fact that domestic resin manufacturers have not unified the grades, so the resin grades are not specifically marked here, but are represented by the conventional resin indicators used in the production of light-transmitting sheets):
Appearance: Colorless/light yellow, clear and transparent Density/g/cm3: 1.12 Solid content%: 57-63
Viscosity (25°C)/MPa. s: 150-250 Refractive index/nD2: 1.53-1.55
Gel time (25°C): 10-16 UV absorber: 3‰
Acid value/mgKOH/g: 27+3 Thermal stability (80°C): ≥24hr
Anti-aging surface
During the forming process of FRP boards, films must be used on the upper and lower surfaces of the boards. The films currently used in China are divided into three-layer co-extrusion films and general polyester films. The three-layer co-extrusion film is to bond the resin and the film tightly together through the chemical layer, which will not be affected by the temperature difference, so as to ensure that the FRP sheet is isolated from water, air and various chemical environments, and has a real anti-aging effect. At the earliest, only DuPont of the United States was supplied to China. Malinex301 and malinex389 have become synonymous with anti-aging films, and this film has the function of blocking ultraviolet rays. This is another misconception. This kind of film does not isolate Ultraviolet rays, to block ultraviolet rays is to rely on the ultraviolet absorber in the resin. However, due to technological monopoly, the price is extremely high, more than 10 US dollars per kilogram.
Therefore, before 2004, more domestic manufacturers were looking for alternatives, that is, using domestically produced polyester films treated with corona. Ordinary polyester films cannot be bonded to FRP sheets, and the principle of this corona-treated film is laser treatment, which produces many bumps on the surface of the film (invisible to the naked eye), increasing the connection interface with the FRP sheet to achieve The film can be bonded with the FRP board as a whole, but the bonding interface achieved by physical means is very unstable, and it is easy to fall off after large changes in cold and heat or after multiple changes in cold and heat. If it is used on roofs and exterior walls, it will increase The hidden danger of water leakage is eliminated, especially U475, U470, SSR480 and other board types are prominent. Many projects fail to waterproof the roof side walls.
After 2004, PT050 and PT055 made in Indonesia entered China. The accelerated aging tester and practice proved that the anti-aging effect is exactly the same, but the price is only half of DuPont's lowest-end products. It is also because of this reason that the anti-aging film technology It is widely used in the country.
At present, there are domestic manufacturers that can produce similar three-layer co-extruded films, and the specific effects are still in the experimental and practical verification. If successful, it will be another big step forward in controlling the cost of the board.
In 2013, Higoal developed a gel coat sprayed surface to replace the aging film. The gel coat has better weather resistance than the aging film, and the aging film has been phased out.
Other auxiliary materials
Most manufacturers now use room temperature curing formula heating rapid prototyping process. The auxiliary materials in the resin formula used in FRP glass steel plates include: curing agent, accelerator, color paste (or color gel coat) and various fillers. In the normal temperature curing formula, methyl ethyl ketone peroxide is generally used as the curing agent; cobalt isooctanoate is used as the accelerator. The participation of cobalt isooctanoate in the reaction has little effect on the color change of the board, and it has outstanding advantages in the production of light-transmitting boards. It is worth mentioning that until now, many manufacturers still have misunderstandings in adding color paste or color gel coat. Generally, they will be diluted with styrene or trichloroethyl phosphate (TCEP), and then added through a proportional pump. Both approaches are wrong. If it is diluted with styrene and added, it will cause the board to become brittle and the strength will decrease, while diluting with TCEP will cause the board to be soft and the weather resistance will decrease (because TECP is an additive flame retardant, it does not participate in the reaction, and it is in the resin There is a polymerization inhibition effect in the polymerization reaction), and it will reduce the adhesion of the anti-aging film. Although the addition amount is not large, it is not advisable in terms of product quality. The correct way is to add the color paste or color gel coat to an appropriate amount of resin and stir evenly, and then add it through a proportional pump.
There are also some manufacturers who use high-temperature curing formulas. The curing agent uses tert-butyl peroxybenzoate (TBPB) or tert-butyl peroxy-2-ethylhexanoate (TBPO). Compared with room-temperature curing formulas, this method produces The board effectively solves the phenomenon of gelation at the high temperature in summer at the resin feeding place of the FRP board production line, but the relative energy consumption is relatively high, and the performance of the final product has little difference.