Laminated glass is a composite glass product made of two or more pieces of glass, with one or more layers of organic polymer interlayer film sandwiched between them. After special high-temperature pre-pressing (or vacuum) and high-temperature high-pressure processing, the glass and interlayer film are permanently bonded together.
Commonly used interlayer films for laminated glass include: PVB, SGP, EVA, PU, etc.
In addition, there are some special types such as colored interlayer laminated glass, SGX type printed interlayer laminated glass, XIR type LOW-E interlayer laminated glass, etc. Laminated glass with embedded decorative elements (metal mesh, metal plates, etc.) and laminated glass with embedded PET materials are also decorative and functional laminated glass.
Laminated glass is increasingly valued for its safety. In the field of architectural glass, EVA, PVB, and SGP are competing fiercely. Today, let's talk about these types of interlayer films.
| EVA
EVA stands for ethylene-vinyl acetate copolymer. It is water-resistant and corrosion-resistant, widely used in foam shoe materials, functional canopy films, packaging films, hot melt adhesives, wires and cables, and toys. In China, EVA is mainly used for making shoe sole materials.
As an interlayer film used in laminated glass, EVA has a lower melting temperature and better fluidity compared to PVB or SGP, generally achieving good processing results around 110°C. Simple vacuum and heating can meet the production needs of EVA laminated glass, and the production equipment only costs around 100,000.
EVA film has good fluidity, suitable for operations such as interlayering and rolling, creating decorative glass with rich patterns, designs, and materials. EVA has good water resistance, but its UV resistance is average, and it tends to yellow and age easily under sunlight.
Currently, EVA laminated glass is mainly used for indoor partitions and decorations, while it is generally not suitable for outdoor curtain walls.
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EVA is widely used in solar panels domestically, but there is a trend abroad to replace EVA with PVB.
From the development history of EVA films, foreign research on EVA films started earlier, and they still have significant advantages in product performance, quality, and production capacity. The domestic EVA film market was once monopolized by foreign brands, with major manufacturers including STR from the USA, Mitsui Chemicals from Japan, Bridgestone, Etimex, etc.
In recent years, with the maturity of domestic EVA technology and lower prices, it has gradually replaced foreign products, and now most EVA films are supplied by domestic manufacturers.
Insiders mentioned that there are about 40 EVA film suppliers in the country, but only about five or six are actually operational, while others are either partially shut down or inactive.
| PVB
PVB stands for polyvinyl butyral, which has high transparency, cold resistance, impact resistance, and UV resistance. PVB is currently the most widely used interlayer material in architectural glass and automotive glass.
Compared to EVA, the storage and processing technology of PVB interlayers is much more complex.
Generally, it is required that the temperature during PVB lamination is between 18-23°C, with a relative humidity of 18-23%, and a moisture content of 0.4%-0.6%. After preheating and rolling or vacuuming, it also needs to be kept under high pressure in an autoclave at 120-130°C and 1.0-1.3MPa for 30-60 minutes.
The complete set of equipment for producing PVB laminated glass costs around 1 million.
PVB laminated glass has good safety, sound insulation, and UV resistance, but PVB's water resistance is poor, and prolonged exposure to moisture can lead to delamination. Seven to eight years ago, PVB films were mainly imported from three major manufacturers: DuPont, Sekisui, and Solvay.
In recent years, domestic PVB has developed rapidly, but most domestic manufacturers use recycled materials for secondary processing, resulting in relatively poor quality stability. There are not many manufacturers that produce PVB starting from the raw material PVA entirely domestically.
On May 24 of this year, SKC signed a letter of intent (LOI) with SVW (a subsidiary of China Petroleum & Chemical Corporation) in Chongqing to establish a joint venture (JV) for PVB film raw materials (resin) and PVB film, aiming to jointly enter the PVB (Polyvinyl Butyral) film market.
The two companies agreed to first set up PVB film production facilities at SKC's film production base in Nantong, Jiangsu Province, and then continue to expand the facilities. SKC will provide PVB film manufacturing technology, while SVW will supply PVB film raw materials.
| SGP
SGP stands for Sentry Glas Plus, an ionic interlayer film developed by DuPont, which has now sold its patents and production lines to Japan's Kuraray.
SGP has high strength and shear modulus, with excellent mechanical properties. The load-bearing capacity of SGP laminated glass is twice that of PVB laminated glass of the same thickness; at the same load and thickness, the deflection of SGP laminated glass is only 1/4 that of PVB laminated glass.
The tear strength of SGP interlayer film is five times that of PVB interlayer film. Even if the glass breaks, the SGP film can still bond the broken glass to form a temporary structure after damage, with small bending deformation and the ability to bear a certain amount of load without falling.
SGP interlayer film has good edge stability and is not sensitive to moisture. SGP interlayer film is colorless and transparent, with good weather resistance and not easily yellowing. The yellowing coefficient of SGP film is less than 1.5, while that of PVB film is 6-12, making SGP more commonly used in ultra-white laminates.
The production process of SGP is similar to that of PVB, and the equipment can be used interchangeably with PVB production equipment. The higher price is the reason for the slower market acceptance of SGP. Solvay (which has been acquired by Eastman Chemical) has a product similar to SGP called DG film, which has low recognition in the domestic market.