Production process of PVB:
Currently,Polyvinyl Butyral Resin (PVB) is mostly produced using an extrusion casting method. China has made some high-end PVB in the past, especially for the military, like in aircraft and military vehicles, but there hasn’t really been a large-scale market for it.
Since the technology behind PVB is a closely guarded trade secret, we don’t have a clear public description of the process. Still, we can get a rough idea from technical documents:
1. First, the raw materials are fed into different extruders by the feeding system, and the pellets are evenly plasticized and molten in the extruder by heating;
2. The molten body passes through the filter to remove impurities;
3. The melted material flows out through the adjustable discharge port after removing the impurities until it cools down and takes shape as a film.
4. The film passes through the automatic X-ray measurement system to see if the thickness meets the technical requirements;
5. After the film goes through processing, it gets treated on the surface, trimmed, wound automatically, and cut into shape. At this point, it's ready as a final product.
For PVB film, it’s important that the surface is flat. If the film is 0.76mm thick, any thickness variation should be no more than 0.02mm. When measuring in both vertical and horizontal directions over a range of 50mm, the error should be under 0.006mm. Also, the moisture content has to stay below 0.3%, and the natural rating should be under 12%.
The technical difficulty of PVB production：
In terms of process, the ratio of polyvinyl butyral resin and plasticizer is one of the key points to determine the quality. In addition, since PVB has high requirements for humidity, special treatment is required during slitting, packaging, storage, and transportation;PVB needs specific humidity levels, so we have to be careful with slitting, packaging, storing, and transporting it. Plus, to make high-quality PVB, we need good resin, which means new projects will need extra resin production areas. This adds some new challenges for managing the process.
For PVB (such as Butvar B-74) in the solar industry, there are extra demands for resistivity and temperature compared to what’s needed for regular car glass or curtain walls. Usually, the resistance furnace requires more than 1000 ohms/cm2; the temperature must be lower than the tolerance temperature of the film to avoid damaging the reaction layer.
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