Why is humidity control critical in glass lamination?

PVB (Polyvinyl Butyral) film is hygroscopic; once its packaging is opened, it takes up or releases moisture until it reaches equilibrium with the room's relative humidity. Glass-to-PVB adhesion depends on film moisture: as moisture rises, adhesion decreases and the risk of bubbles, haze and edge delamination increases. To keep film moisture at about 0.4–0.5%, PVB manufacturers recommend about 16–20 °C and 22–30% RH in the lay-up room; common practice is 18–20 °C and 25–30% RH.

What should be the target dew point in a glass lamination room?

The dew point follows from the room temperature and relative humidity target. 18 °C / 25% RH corresponds to a dew point of about −2 °C, and 20 °C / 30% RH to about +2 °C; in other words, a lay-up room needs a dew point around 0 °C. Since the practical lower limit of condensation dehumidifiers is about +5 °C dew point, silica gel rotor dehumidifiers are used in these rooms.

How long can PVB film be used after opening?

Once removed from its original packaging, PVB film starts exchanging moisture with the room; if room humidity is above the target band, film moisture rises. According to PVB manufacturers' guides, refrigerated rolls brought into a lay-up room at 8 °C or above should be unwound and processed or cut within 2–3 hours. The exact time should be taken from the film manufacturer's guide; unused sections should be returned to moisture-barrier packaging.

What is the difference between silica gel rotor and condensation dehumidifiers?

Condensation (compressor-based) dehumidifiers condense moisture by cooling air below its dew point; their practical lower limit is about +5 °C dew point (≈ 37% RH at 20 °C), and their efficient range is +10 °C dew point and above. Silica gel rotor dehumidifiers hold moisture by physical adsorption on silica gel and reach very low dew points regardless of temperature. Since a PVB lay-up room needs a dew point around 0 °C, a silica gel rotor unit is required; with humid summer outdoor air, a hybrid configuration with a cooling coil ahead of the rotor saves energy.

How often should humidity calibration be performed in a clean room?

Humidity sensors are typically verified or calibrated against a traceable reference every 6–12 months; on lines operating within a narrow target band, the interval can be shortened. Calibration results should be documented and linked to production quality records. The exact interval is set by the plant's quality system.

Is a controlled room also required for SentryGlas (SGP) interlayer?

According to its manufacturer, SentryGlas is less susceptible to moisture, weathering and edge defects than PVB. Even so, because dust and fibers cause optical defects between glass and film, a clean and controlled lay-up environment is needed; temperature and humidity are set according to the product's processing guide. If PVB is also processed on the same line, room conditions are chosen for PVB.

What is the optimal humidity range for my production line?

For PVB lines, manufacturer guidance is about 16–20 °C and 22–30% RH; common practice is 18–20 °C and 25–30% RH. Above the band, film moisture rises and adhesion drops; humidity that is too low can make adhesion excessive and encourages static charge and dust attraction on the film. The exact target is set by the processing guide of the PVB type used and the product's pummel target.

Can I retrofit a TFT – Italy dehumidifier to my existing lamination room?

Yes, a silica gel rotor dehumidifier can be added to an existing lay-up room. Unit selection requires the room volume, fresh air flow, target temperature and humidity, and information on the existing ventilation system. With this data, NKT provides technical support in selecting a suitable TFT unit and supplies it; installation and ductwork are carried out by the plant's mechanical contractor.

How should opened PVB rolls be stored?

According to PVB manufacturers' guides, opened refrigerated rolls should be stored at ≤ 8 °C and 25–30% RH, and opened PE-interleaved rolls at ≤ 18 °C and 25–30% RH. Sealed rolls need no humidity control; refrigerated rolls are kept at ≤ 8 °C and PE-interleaved rolls at ≤ 30 °C. A room for opened rolls, like the lay-up room, needs a low dew point and is conditioned with a silica gel rotor dehumidifier.

Which standards apply to glass lamination production?

The core series for laminated glass is EN ISO 12543: Part 1 definitions and component parts, Part 2 laminated safety glass, Part 3 laminated glass, Part 4 test methods for durability (high temperature, humidity and radiation), Part 5 dimensions and edge finishing, Part 6 appearance. EN 12600 covers impact safety, EN 356 manual attack resistance, and ISO 14644-1 cleanroom classification. Lay-up room conditions, however, are defined not by a standard but by the interlayer manufacturer's processing guide.

Technical Article31 min read

Humidity Control in Glass Lamination: The Key to Quality

In laminated glass, glass-to-PVB adhesion depends on the film's moisture content. PVB manufacturers recommend about 16–20 °C and 22–30% RH for the lay-up room; since the dew point of these conditions is around 0 °C, silica gel rotor dehumidification is required.

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Related Glossary Terms

For deeper definitions of the technical concepts in this article, browse the related entries in the NKT Glossary:

Relative Humidity (RH)Moisture Content (Specific Humidity)Moisture Load Dew Point Silica Gel Rotor (Desiccant Rotor)Reactivation (Regeneration)Adsorption Infiltration Calibration ACH (Air Changes per Hour)HEPA Filter (High-Efficiency Particulate Air)ISO 14644 (Cleanroom Classification)Hygroscopic (Moisture-Attracting)Sorption (Adsorption + Absorption)PVB (Polyvinyl Butyral)Static Electricity Humidification Capacity (kg/h)Humidity Ratio (x)Silica (SiO₂)Filtration (Water Filtration)Humidity Sensor

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