PVB - Polyvinyl Butyral
Laminated, or safety, glass consists of two or more plies of glass (annealed or tempered) bonded together by interlayers of polyvinyl butyral (PVB).
During the laminating process, the glass is subjected to a pressure of 180 to 200 PSI and a temperature of between 275° and 300°F in an autoclave to ensure solid adhesion of the various layers.
When laminated glass is fractured, the PVB interlayer acts as a shield, retaining the fragments of glass and affording protection of the area until the unit can be replaced.
Typical Properties:
• PVB thickness --0.38mm, 0.76mm, 1.14mm, 1.52mm
• PVB colors --Clear, white, gray, purple, blue, green, yellow, orange, red
• Refractive Index -- 1.48
• Visible Light Transmittance, Clear -- 89%
• Shading Coefficient, Clear -- 0.92
• UV Screening, up to 380 nm -- 99%
• Tensile Strength -- 3220 psi
• Tensile Elongation -- 205% (JIS K6771)
• Specific Gravity -- 1.07
• Specific Heat -- 0.47 Btu/lb°F
• Thermal Conductivity (K value) -- 0.12 Btu/(ft2hr°F)
• Coefficient of Thermal Expansion -- 2.6 x 10-4 in./in.°F
• Emissivity -- 0.9
Acoustic Performance:
Normal monolithic glass achieves typical weighted reductions in noise trasfer through its realtive mass, i.e.:
3mm provides an Rw of 29dB
6mm provides an Rw of 31dB
12mm provides an Rw of 34 dB
Although it should be noted that when combining similar glass lites to form a unit, the weighted reduction is not greatly improved, i.e.:
6mm / 12mm air / 6mm provides an Rw of 33 dB (note less than 12mm above)
Laminated glass improves the sound insulation properties of glass due to the resilient interlayer sandwiched between the glass which provides damping at coincident and higher frequencies, and because it improves the impedance of glass.
6.8mm provides an Rw of 32 dB, however
6.8mm acoustic laminate - PVB (A) provides an Rw of 35 dB
PVB (A) film, such as Stadip Silence by Saint Gobain, improves the acoustic insulating performance of glass at the critical frequency.
During the laminating process, the glass is subjected to a pressure of 180 to 200 PSI and a temperature of between 275° and 300°F in an autoclave to ensure solid adhesion of the various layers.
When laminated glass is fractured, the PVB interlayer acts as a shield, retaining the fragments of glass and affording protection of the area until the unit can be replaced.
Typical Properties:
• PVB thickness --0.38mm, 0.76mm, 1.14mm, 1.52mm
• PVB colors --Clear, white, gray, purple, blue, green, yellow, orange, red
• Refractive Index -- 1.48
• Visible Light Transmittance, Clear -- 89%
• Shading Coefficient, Clear -- 0.92
• UV Screening, up to 380 nm -- 99%
• Tensile Strength -- 3220 psi
• Tensile Elongation -- 205% (JIS K6771)
• Specific Gravity -- 1.07
• Specific Heat -- 0.47 Btu/lb°F
• Thermal Conductivity (K value) -- 0.12 Btu/(ft2hr°F)
• Coefficient of Thermal Expansion -- 2.6 x 10-4 in./in.°F
• Emissivity -- 0.9
Acoustic Performance:
Normal monolithic glass achieves typical weighted reductions in noise trasfer through its realtive mass, i.e.:
3mm provides an Rw of 29dB
6mm provides an Rw of 31dB
12mm provides an Rw of 34 dB
Although it should be noted that when combining similar glass lites to form a unit, the weighted reduction is not greatly improved, i.e.:
6mm / 12mm air / 6mm provides an Rw of 33 dB (note less than 12mm above)
Laminated glass improves the sound insulation properties of glass due to the resilient interlayer sandwiched between the glass which provides damping at coincident and higher frequencies, and because it improves the impedance of glass.
6.8mm provides an Rw of 32 dB, however
6.8mm acoustic laminate - PVB (A) provides an Rw of 35 dB
PVB (A) film, such as Stadip Silence by Saint Gobain, improves the acoustic insulating performance of glass at the critical frequency.
Performance of PVB under high temperature
PVB is a solid resin which is soluble in organic solvents but not in hydrocarbons and which is resistant to acids and alkalis. Interlayer used in construction are normally made from resins. 20 % of their hydroxyl groups are free what results in a good adhesive strength. The adhesion between the glass and the layer is based on the formation of hydrogen bonds. Layers from PVB show high stiffness which can be reduced by adding plasticiser (such as adipic acid or polyethylene glycol). This is related with an increasing of elasticity and adhesive power of the material.
Ionic polymers can be synthesized through connection of ionic groups to the polymer backbone. Depending on the concentration of ionic groups within the polymer, the products are differentiated between polyelectrolyte and ionomers. Ionomers have an ionic content of at most 10% within a non-polar polymer. These ionic groups are partly or complete neutralized to build salts. In 1964 DuPont introduced the term “ionomer” for the first time to characterize this type of materials.
The thermogram of polyvinyl butyral shows different stages of decomposition. A first small step can be found at about 100 °C with a mass loss of about 0.5 %. This stage can be explained with evaporating of water from the interlayer. The next step starts at about
150 °C and ends at 330 °C with a mass loss of 27 %. The third and last stage with a mass loss of 72 % takes place between 320 °C and 420 °C. Here the entire polymer backbone decomposes.
In contrast, the thermogram of the ionomer shows only one stage from 350 °C to 600 °C. The mass loss is 96 %. Within this temperature range the entire polymer backbone decomposes. The remaining mass of about 4 % corresponds with the amount of metalions in the polymer.
Ionic polymers can be synthesized through connection of ionic groups to the polymer backbone. Depending on the concentration of ionic groups within the polymer, the products are differentiated between polyelectrolyte and ionomers. Ionomers have an ionic content of at most 10% within a non-polar polymer. These ionic groups are partly or complete neutralized to build salts. In 1964 DuPont introduced the term “ionomer” for the first time to characterize this type of materials.
The thermogram of polyvinyl butyral shows different stages of decomposition. A first small step can be found at about 100 °C with a mass loss of about 0.5 %. This stage can be explained with evaporating of water from the interlayer. The next step starts at about
150 °C and ends at 330 °C with a mass loss of 27 %. The third and last stage with a mass loss of 72 % takes place between 320 °C and 420 °C. Here the entire polymer backbone decomposes.
In contrast, the thermogram of the ionomer shows only one stage from 350 °C to 600 °C. The mass loss is 96 %. Within this temperature range the entire polymer backbone decomposes. The remaining mass of about 4 % corresponds with the amount of metalions in the polymer.
SentryGlas Plus Laminate
Stronger than conventional laminating materials, SentryGlas® Plus interlayers help create safety glass that protects against bigger storms, larger impacts, and more powerful blasts. They become an engineered component within the glass, holding more weight, so the glass can serve as a more active structural element in the building envelope. And they do all of this while increasing framing system design freedom and improving long-term weather resistance.
SentryGlas® Plus is 100 times stiffer and 5 times stronger than traditional interlayers, helping thinner laminates meet specified wind loads or structural requirements.
In stairs, flooring and overhead glazing, laminated glass made with SentryGlas® Plus acts like an engineered composite, with low mechanical strain under loads, and outstanding post-breakage resistance to creep and collapse.
SentryGlas® Plus is 100 times stiffer and 5 times stronger than traditional interlayers, helping thinner laminates meet specified wind loads or structural requirements.
In stairs, flooring and overhead glazing, laminated glass made with SentryGlas® Plus acts like an engineered composite, with low mechanical strain under loads, and outstanding post-breakage resistance to creep and collapse.
Edge Delamination
Source: http://www.aisglass.com/laminated-glass/AIS-82.pdf
Despite the long history of the use of laminated glass in buildings there is concern with some architects on the potential for serious delamination issues with laminated glass.
Delamination issues with laminated glass made using PVB interlayers fall into two main categories:
• Sunburst delaminations
This type of delamination is generally the result of poor manufacturing processes, which impart stresses at locations at the edges of laminated glass, often combined with thinning of the PVB. Optical distortion is also normally evident at these locations. The most common cause of this type of localized delamination is the use of clamping devices on the edges of laminated tempered glass during the autoclaving of the laminated glass. While the quality of the glass may appear to be satisfactory at time of dispatch of the glass from the factory gradual release over time of the stresses imparted to the glass at the locations that were clamped may result in ‘sunburst’ delaminations.
• Edge delamination
Edge stability is defined as the laminate’s resistance over time to form defects along the edge. Unfortunately projects in which edge delamination of around 12 mm has been observed have raised concern with some architects and specifiers about the edge stability of laminated glass in general. On the other hand there are many installations of laminated glass containing B14 PVB interlayer having exposed edges and silicone butt-joined edges that exhibit zero edge defects or only a few minor edge defects many years after installation.
Extract from Dupont investigation into PVB edge delamination
‘Sunburst’ Delamination
‘Sunburst’ delamination have undoubtedly caused concern in the glazing industry. This type of delamination is generally the result of poor manufacturing processes, which impart stresses at locations at the edges of laminated glass, often combined with thinning of the PVB. Optical distortion is also normally evident at these locations.
The most common cause of this type of localised delamination is the use of clamping devices on the edges of laminated tempered glass during the autoclaving of the laminated glass. While the quality of the glass may appear to be satisfactory at time of dispatch of the glass from the factory gradual release over time of the stresses imparted to the glass at the locations that were clamped may result in ‘sunburst’ delamination.
Extract from: FUNDAMENTALS OF LAMINATING PROCESS AND QUALITY REQUIREMENTS by Dr. Gérard F. Savineau
Impact, adhesion to glass, moisture content of the PVB interlayer, thickness of the PVB, float glass orientation, glass treatment (metal coated, chemically tempered, colour), residual salts on the glass surface, glass surface contamination, are all important variables that control final performance:
For a given glass type and thickness, impact levels will vary inversely with adhesion:
Impact = f (1/adhesion)
The thicker the PVB the higher the impact:
Impact= f (PVB thickness)
Moisture in the PVB interferes with the glass/PVB bonding mechanism. Thus as moisture content increases, the adhesion drops and the impact improves:
Adhesion = f (1/% moisture)
Impact = f (% moisture)
Too high moisture content may result in bubble formation and/or delamination with time.
The placement of the air side of the float glass against the PVB will result in higher adhesion than the tin side
High residual salt concentration on the glass surfaces at lamination, interferes with bonding and lower the adhesion.
Adhesion to metal coated glass depends on the coating and requires to be studied case by case.
Any glass surface contamination at the assembly step may result in unacceptable visual and/or optical quality.
Inadequate de-airing steps and/or autoclave cycle may result in trapped air penetration and consequently delamination or bubble formation even if not directly visible at the inspection.
Extract from Glass performance days 2015 research into acoustic interlayers
Field defect in laminated acoustic glazing
With the introduction of the tri-layer acoustic PVB, the glass manufacturers and their customers are faced with a problem that is not detectable during the lamination process, but later in the field inspection. This defect, which is called “ice-flowers”, is rather complicated because it is a delayed defect that will appear typically after exposure to changing climate conditions, and therefore may create a lot of claims and external waste costs.
The route-cause of this defect starts in the early stage of the lamination process with tri- layer. During the de-airing process some amount of trapped air cause little and not easy detectable bubbles in the PVB, which can be named as “supersaturating” phenomena. Small amounts of trapped air will under changing climate conditions start to penetrate through the tri-layer and accumulate into one region of the laminated glass causing visible bubbles. In the final step those bubbles will become visible as “ice- flowers”.
Despite the long history of the use of laminated glass in buildings there is concern with some architects on the potential for serious delamination issues with laminated glass.
Delamination issues with laminated glass made using PVB interlayers fall into two main categories:
• Sunburst delaminations
This type of delamination is generally the result of poor manufacturing processes, which impart stresses at locations at the edges of laminated glass, often combined with thinning of the PVB. Optical distortion is also normally evident at these locations. The most common cause of this type of localized delamination is the use of clamping devices on the edges of laminated tempered glass during the autoclaving of the laminated glass. While the quality of the glass may appear to be satisfactory at time of dispatch of the glass from the factory gradual release over time of the stresses imparted to the glass at the locations that were clamped may result in ‘sunburst’ delaminations.
• Edge delamination
Edge stability is defined as the laminate’s resistance over time to form defects along the edge. Unfortunately projects in which edge delamination of around 12 mm has been observed have raised concern with some architects and specifiers about the edge stability of laminated glass in general. On the other hand there are many installations of laminated glass containing B14 PVB interlayer having exposed edges and silicone butt-joined edges that exhibit zero edge defects or only a few minor edge defects many years after installation.
Extract from Dupont investigation into PVB edge delamination
‘Sunburst’ Delamination
‘Sunburst’ delamination have undoubtedly caused concern in the glazing industry. This type of delamination is generally the result of poor manufacturing processes, which impart stresses at locations at the edges of laminated glass, often combined with thinning of the PVB. Optical distortion is also normally evident at these locations.
The most common cause of this type of localised delamination is the use of clamping devices on the edges of laminated tempered glass during the autoclaving of the laminated glass. While the quality of the glass may appear to be satisfactory at time of dispatch of the glass from the factory gradual release over time of the stresses imparted to the glass at the locations that were clamped may result in ‘sunburst’ delamination.
Extract from: FUNDAMENTALS OF LAMINATING PROCESS AND QUALITY REQUIREMENTS by Dr. Gérard F. Savineau
Impact, adhesion to glass, moisture content of the PVB interlayer, thickness of the PVB, float glass orientation, glass treatment (metal coated, chemically tempered, colour), residual salts on the glass surface, glass surface contamination, are all important variables that control final performance:
For a given glass type and thickness, impact levels will vary inversely with adhesion:
Impact = f (1/adhesion)
The thicker the PVB the higher the impact:
Impact= f (PVB thickness)
Moisture in the PVB interferes with the glass/PVB bonding mechanism. Thus as moisture content increases, the adhesion drops and the impact improves:
Adhesion = f (1/% moisture)
Impact = f (% moisture)
Too high moisture content may result in bubble formation and/or delamination with time.
The placement of the air side of the float glass against the PVB will result in higher adhesion than the tin side
High residual salt concentration on the glass surfaces at lamination, interferes with bonding and lower the adhesion.
Adhesion to metal coated glass depends on the coating and requires to be studied case by case.
Any glass surface contamination at the assembly step may result in unacceptable visual and/or optical quality.
Inadequate de-airing steps and/or autoclave cycle may result in trapped air penetration and consequently delamination or bubble formation even if not directly visible at the inspection.
Extract from Glass performance days 2015 research into acoustic interlayers
Field defect in laminated acoustic glazing
With the introduction of the tri-layer acoustic PVB, the glass manufacturers and their customers are faced with a problem that is not detectable during the lamination process, but later in the field inspection. This defect, which is called “ice-flowers”, is rather complicated because it is a delayed defect that will appear typically after exposure to changing climate conditions, and therefore may create a lot of claims and external waste costs.
The route-cause of this defect starts in the early stage of the lamination process with tri- layer. During the de-airing process some amount of trapped air cause little and not easy detectable bubbles in the PVB, which can be named as “supersaturating” phenomena. Small amounts of trapped air will under changing climate conditions start to penetrate through the tri-layer and accumulate into one region of the laminated glass causing visible bubbles. In the final step those bubbles will become visible as “ice- flowers”.