Definition
A transparent, flexible thermoplastic interlayer placed between two glass layers in laminated glass production. Used in automotive windshields, architectural facades, solar panels, and safety glass applications. PVB is hygroscopic; manufacturers target a film moisture of about 0.4–0.5% at lay-up. To achieve this, the lay-up room is kept at about 16–20 °C and 22–30% RH (dew point around 0 °C), a condition provided by silica gel rotor dehumidifiers.
Detailed Explanation
PVB (Polyvinyl Butyral) is obtained from the reaction of polyvinyl alcohol with butyraldehyde. Eastman, Kuraray, and Sekisui are leaders in the global market.
Properties: • Optical clarity (>95% light transmission) • High flexibility (holds glass pieces if shattered) • UV protection (significantly blocks UV) • Acoustic insulation • Hygroscopic (manufacturer target ≈ 0.4–0.5% film moisture)
Production process: 1. PVB is stored in its original moisture-barrier packaging: refrigerated rolls ≤ 8 °C, PE-interleaved rolls ≤ 30 °C (Kuraray manual) 2. It is laid up at about 16–20 °C and 22–30% RH; refrigerated rolls in a room above 8 °C are processed within 2–3 hours 3. Two glass layers + PVB sandwich is assembled 4. Pre-bonding (de-airing: nip rollers or vacuum + heat) 5. Autoclave (high temperature and pressure; glass temperature at least ≈ 125 °C) → permanent bond
Moisture equilibrium (manufacturer curves): • 30% RH → film moisture ≈ 0.35–0.45% • 50% RH → ≈ 0.7–0.8% (adhesion drops; risk of bubbles and edge delamination rises) • Humidity too low → adhesion can become excessive; static charge and dust attraction increase
Adhesion is measured with the pummel test: the sample is broken with a hammer at ≈ −18 °C and the glass still adhering to the PVB is rated on a 0–10 scale; higher film moisture lowers the pummel value.
Engineering Note
Four key points for a PVB lay-up room:
1. Target band — manufacturer guidance ≈ 16–20 °C and 22–30% RH; common practice 18–20 °C and 25–30% RH. The dew point of these conditions is ≈ −2…+2 °C (18 °C / 25% RH → −2.3 °C; 20 °C / 30% RH → +1.9 °C).
2. Technology — since the practical lower limit of condensation units is ≈ +5 °C dew point, a silica gel rotor unit is required; with humid summer air, a hybrid configuration with a cooling coil ahead of the rotor saves energy.
3. Load — the largest component is usually fresh air: bringing 17 g/kg summer air down to 20 °C / 30% RH (4.3 g/kg) means ≈ 15 kg/h of moisture removal per 1,000 m³/h. Safety margin 15–25%.
4. Static electricity — do not let humidity drop below the target band; ionization if needed.
NKT supplies TFT AD and ADP series silica gel rotor and Hybrid dehumidifiers for glass lamination rooms and provides technical support in unit selection.
