Humidity Control in the Glass Industry: A Primordial Strategy
Achieving the required quality and durability for all types of glass demands more than just premium raw materials. Manufacturers and processors must meticulously manage the ambient climate, as uncontrolled variations in temperature and humidity can lead to significant product damage.
The glass industry, a rapidly evolving, high-technology sector, faces acute challenges related to temperature and moisture management. Inadequate relative humidity (RH) at various points in the production and storage cycle can result in substantial losses concerning product quality, efficiency, and financial outcomes. Thermomatic, specializing in HVAC-R engineering, positions itself as the essential strategic partner, delivering advanced moisture control systems to guarantee product excellence and long-term durability in glass manufacturing.
Glass and the Chemical Challenge of Moisture
Despite its seemingly inert and impermeable nature, glass is not immune to atmospheric moisture. As an amorphous vitreous material, its surface continuously engages in a chemical reaction with airborne water and CO₂ molecules, resulting in the formation of a microscopic, hydrophilic silanol layer (Si–OH). This initial surface change is the catalyst for virtually all subsequent humidity-related defects in the glass industry.
In essence, the glass surface "exchanges" with its environment: it both adsorbs and desorbs water molecules, a process which fundamentally impairs adhesion, transparency, and optical stability, often initiating delamination.
This micro-hydrolysis process actively degrades chemical bonds and diminishes the surface energy—the exact conditions required for PVB, EVA, or TPU interlayers to achieve their maximum bonding strength.
Key Defects Triggered by Moisture in Glass Manufacturing
Improper humidity levels can cause a range of harmful phenomena and consequences:
Surface Hydrolysis: Reaction of silica (SiO₂) with H₂O forming silanol. Causes loss of gloss, milky stains (irisation), and reduced adhesion with PVB/EVA films;
Interlaminar Condensation: Moist air trapped between layers (PVB, EVA, TPU) leads to delamination and bubbles, resulting in transparency loss and optical failure;
Hygroscopic Absorption in PVB/EVA: Polymers absorb humidity from the air (up to 0.4% H₂O in 24h at 60% RH). This causes dimensional variation and adhesion loss, responsible for up to 70% of lamination rejects;
Alkaline Corrosion (“Stain” or “Irisation”): Na⁺ ions migrate from the glass matrix under high RH and temperature, resulting in iridescence, opacity, and surface stains, common in mirrors and stored glass;
Microcondensation During Storage: Thermal fluctuations combined with high RH cause “fogging” stains on tempered and laminated glass, resulting in irreversible aesthetic damage.
Vulnerability Analysis: Moisture's Effect on Specific Glass Types
Every glass formulation possesses unique vulnerabilities and sensitivities to moisture, necessitating tailored environmental control strategies.
Flat Glass (Float Glass)
Float glass is particularly susceptible to both moisture and airborne contaminants. When stacked without adequate separation, condensation forming between the sheets can rapidly lead to irisation (rainbow-like staining) and alkaline corrosion. These defects result in permanent surface marks and a measurable reduction in optical transparency.
Ideal Conditions: Iridescence is triggered when the air's dew point surpasses the glass surface temperature. For instance, environments at 60% RH and 25°C can create the conditions for condensation during thermal shifts, initiating the corrosive process.
Laminated Glass
Composed of two or more glass layers bonded with an interlayer (PVB, EVA, or ionoplast), laminated glass is extremely sensitive to humidity. Polymers such as PVB and SentryGlas® are hygroscopic and absorb moisture from the air, interfering with adhesion and causing delamination, bubbles, cloudy stains, and loss of structural bonding.
Ideal Conditions:The lamination assembly room should maintain relative humidity between 20%–25% RH (±5%), not exceeding 30% RH. PVB rapidly absorbs moisture, reaching equilibrium with the environment in approximately two hours.
Tempered Glass
Produced through heating and rapid cooling, tempered glass requires strict temperature and humidity control during processing and cooling. Condensation on hot surfaces can cause post-tempering irisation, surface corrosion, and white stains, compromising both strength and aesthetics.
Wired Glass
Contains an embedded metal mesh that creates zones of condensation and differential oxidation when exposed to humidity. This can lead to internal wire corrosion, surface irisation, and delamination between the wire and glass.
Insulated (Double) Glass
Composed of glass panes separated by a dehydrated or inert gas chamber, insulated glass is vulnerable to moisture infiltration. Humidity entering the chamber causes internal fogging, low-E coating corrosion, and spacer oxidation, compromising thermal and acoustic insulation.
Bulletproof (Multilayered) Glass
Made from multiple glass and polymer layers, its ballistic integrity depends on interlayer adhesion, which is highly sensitive to humidity. Moisture absorption in polymers reduces cohesion, causing delamination, opacification, and decreased ballistic performance.
Consequences: Delamination in bulletproof glass can reduce ballistic resistance by 15–20%, leading to significant financial losses.
Mirrors
Flat glass with metallic and protective coatings on the back side, mirrors are highly susceptible to humidity-induced oxidation. This causes black spots (“black edge”), reflective film detachment, and loss of brightness.
Thermomatic Solution – Precision Air Engineering
Thermomatic offers high-accuracy HVAC-R systems for humidity control, redefining production standards in the glass and armor industries. The solutions are designed to meet the specific needs of each process stage, ensuring product quality and durability.
Comparison of Dehumidification Systems for Glass
The glass industry primarily utilizes two distinct dehumidification technologies, each suited for different stages of the manufacturing process:
Condensation Dehumidifiers – Industrial Plus Line:
Ideal for environments where the temperature is not excessively low and humidity must be reduced to moderate levels (e.g., 40–60% RH). They work by thermal shock, condensing moisture to prevent reaching the dew point.
IThey are energy-efficient, providing lower operational costs (OPEX) and reduced capital expenditure (CAPEX).
Desiccant Dehumidifiers – Desiccant Line:
These use a desiccant material (silica wheel) to adsorb moisture from the air. They are effective in achieving very low humidity levels (below 20–30% RH) and operate efficiently in cooler environments. They are essential for processes such as glass lamination with PVB/EVA. These more demanding conditions require higher CAPEX and OPEX investment, but payback is achieved through a significant reduction in lamination rejects.
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Benefits and Return on Investment (ROI)
Benefits
Implementing Thermomatic solutions results in tangible benefits and a fast return on investment:
Elimination of Bubbles and Delamination: Scrap reduction of up to 60%;
Perfect Transparency and Adhesion: Guaranteed aesthetic and functional quality;
Dimensional and Optical Stability: Preservation of intrinsic material characteristics;
Extended Life Cycle of Bulletproof Glass: Maintains ballistic resistance and safety;
Reduced Losses: Average losses from delamination (3–7%) and irisation/alkaline corrosion (up to 12%) are drastically minimized.
ROI
Partnership for Glass Industry Excellence
Thermomatic is more than an equipment supplier; it is a strategic partner that understands the nuances of the glass industry and provides customized solutions to ensure maximum quality, safety and efficiency.
Invest in precise humidity and temperature control and elevate your production standards.
Contact our specialists to schedule a technical visit and discover how Thermomatic’s solutions can transform your glass production line.
FAQs
PVB detachment, a process known as delamination, occurs primarily due to the presence of moisture during the glass lamination process, whether on the glass surface or in the interlayer itself (PVB, EVA) before the autoclave cycle for laminated glass.
The chemical cause lies in the surface hydrolysis of the glass: the material reacts with water (H₂O) in the air, forming silanol groups (Si–OH), which reduce the surface energy and hinder adhesion. Since PVB and ionoplast are hygroscopic polymers, they absorb this moisture; during the autoclave's thermal cycle, the water turns into vapor, creating interlaminar pressure that separates the layers and creates bubbles between the laminated glass, stains, and film detachment.
Besides moisture, other causes include contamination by dust or grease on the sheets and improper storage. To ensure perfect adhesion, it is essential that the lamination room and the PVB chamber maintain strict control of relative humidity, ideally between 22% and 25% RH, with a stable temperature of 68–73 °F and controlled positive pressure. Using temperature and humidity control in the autoclave allows for maintaining a low dew point and completely eliminating the risk of condensation.
Bubbles between laminated glass layers and delamination are defects mostly caused by moisture in the glass lamination, absorbed by the interlayer (PVB, EVA) before autoclaving. The presence of water, even at microscopic levels, prevents complete adhesion between the polymer and the glass. In tests, a variation of just 0.2% in the moisture content of the PVB can reduce the adhesion strength (shear energy) by up to 30%.
Common factors leading to this problem include PVB absorbing water, exposure of the interlayer to environments with relative humidity above 30% during assembly or storage, condensation on the glass surface – which occurs when the glass temperature is below the ambient dew point – and excessive time between assembling the "sandwich" (glass + PVB + glass) and loading it into the autoclave, allowing the assembly to absorb moisture from the air.
Preventive control should maintain RH below 25%, with temperature stabilized at 68–73 °F and a constant flow of dry air, ensuring perfect adhesion and reducing scrap rates on the lamination line.
Stains, opacity, and especially iridescence (a rainbow-like effect on the surface) are defects directly linked to moisture in glass lamination. Iridescence, also known as alkaline corrosion, occurs when moisture on the glass surface causes the migration of alkaline ions (Na⁺ and K⁺) from within the glass structure to the surface. This generates deposits that alter light refraction, creating the rainbow effect.
The problem is intensified under conditions of high relative humidity and temperature during storage, especially when there is no temperature and humidity control in the autoclave or when the process ignores the ideal conditions of the lamination room.
Stains and opacity (a milky appearance) are caused by moisture absorbed by the interlayer (PVB/EVA), which compromises adhesion and transparency, resulting in a "milky" look or localized stains. Condensation between stacked glass sheets without proper spacers is a common cause.
The ideal is to maintain relative humidity around 45–55% in storage and finishing areas, preventing both iridescence and late delamination.
Preventing delamination in ballistic glass is a critical safety issue, and the process requires even stricter environmental control. The root cause is the same as for common laminated glass: moisture in the glass lamination, absorbed by the interlayer (PVB, polycarbonate, etc.).
However, in a ballistic composition, delamination is not just a cosmetic defect; it compromises the assembly's ability to dissipate the energy of an impact, drastically reducing ballistic protection.
Documented cases show that variations above 30% RH in the assembly area can cause late delamination at the edges of the ballistic glass weeks after curing, especially when storage occurs in areas without controlled climate.
To avoid this problem, it is mandatory that all steps – from interlayer storage to assembly and curing – occur in rooms meeting the ideal conditions for a lamination room, with controlled relative humidity (ideally below 30%) and air filtration systems to avoid contamination by particles, which can also create points of adhesion failure.
To avoid stains, iridescence, or late delamination, the storage of glass (laminated or not) must be done in a controlled environment. Storing in locations without proper temperature and humidity control for autoclaving or without a climate control system for a glass factory increases the risk of defects by up to 70%.
The ideal conditions for the lamination room or storage area are:
Relative Humidity of 40% to 55%;
Temperature of 68 °F to 77 °F;
Ventilation with constant airflow and renewal to prevent pockets of humid air;
Stacking always using spacers between the sheets to allow air circulation and prevent direct contact that can cause condensation.
Controlling these environmental parameters is essential to prevent alkaline corrosion and preserve the optical clarity of the stored glass.
Yes, this is expected behavior. PVB absorbing water is a normal phenomenon because it is a hygroscopic polymer—it naturally absorbs moisture during the glass lamination process. This absorption is not a defect but a physico-chemical characteristic of the material.
The problem arises when the moisture content exceeds the limit of 0.5%, which compromises its viscosity and, most importantly, its adhesion capability to the glass. Therefore, storage and handling must take place in an environment with humidity control for PVB lamination, maintaining Relative Humidity (RH) between 20% and 30% and a stable temperature of 68–73°F.
This control ensures dimensional stability of the interlayer and predictable performance during the autoclave cycle.
To ensure maximum adhesion and optical integrity, the ideal parameters for a glass lamination room using PVB are:
Relative Humidity (RH) of 20% to 25%, this being the most critical factor, and never exceeding 30%.
Temperature of 64°F to 68°F, with controlled fluctuations of no more than ±2°F.
Temperature and humidity control in the autoclave to ensure psychrometric stability and completely eliminate the risk of condensation on the glass surface.
Positive pressure of +5 Pa, following the ideal lamination room conditions, preventing the infiltration of humid and contaminated air.
These parameters ensure uniform adhesion, prevent delamination, and maintain the dew point at least 18°F below the ambient temperatur.
Even with the correct autoclave cycle (pressure and temperature), adhesion can fail if there is moisture present during the assembly stage of the glass lamination. The autoclave cycle does not "eliminate" moisture; it only forces adhesion under pressure and heat.
If water is present between the layers, it turns into vapor, creating internal pressure that competes with the autoclave pressure, preventing complete adhesion. Besides moisture, other causes include contamination of the glass surface by dust, grease, or chemical residues, which create a physical barrier and prevent molecular contact between the PVB and the glass.
Another critical factor is temperature and humidity control in the autoclave, as parameters outside the ideal range compromise adhesion and favor defects like bubbles in laminated glass. Minimizing the time between pre-sealing and autoclaving is essential, as every minute of exposure to ambient air is an opportunity for the PVB to absorb water, reducing lamination quality and the optical durability of the glass.
The dew point is the temperature at which the air reaches 100% moisture saturation and begins to condense water into droplets. In the glass lamination room, if the surface of the glass or the interlayer is colder than the dew point of the ambient air, the moisture in the air will condense on them, creating a film of water invisible to the naked eye, but sufficient to cause bubbles in laminated glass, delamination, and stains.
For example, if the room's dew point is 59°F and a newly cut glass sheet is at 54°F, immediate condensation will occur. This is why temperature and humidity control in the autoclave is as important as controlling relative humidity.
The ideal is to maintain the dew point at least 18°F below the ambient temperature, ensuring psychrometric stability, absence of condensation, and perfect adhesion during lamination.
The cloudy appearance (diffuse opacity) is a classic symptom of moisture in the glass lamination, absorbed by the interlayer or condensed at the glass-PVB interface. Even microscopic amounts of water can create a molecular separation layer that scatters light, generating the milky effect. This defect is permanent and cannot be corrected after curing.
The main causes include PVB absorbing water, condensation during pre-sealing due to the temperature difference between the glass and the environment, and excessive time between assembly and autoclaving in an environment without temperature and humidity control for the autoclave.
Keeping the assembly room within the ideal conditions of the lamination room is essential to eliminate the risk of condensation, ensure transparency, and guarantee perfect adhesion between the layers.
Once delamination has occurred, full recovery is impossible—the panel must be remade.
However, the cause can and should be diagnosed:
If it occurred within less than 3 months, the origin is high moisture in the glass lamination process within the PVB/EVA;
If it occurred after years of use, the problem may be due to improper installation or water infiltration.
The best practice is to perform a PVB moisture absorption test and review the clean room conditions (humidity, temperature, and ventilation).
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