Saflex QS31

Saflex QS31 is specified in laminated safety glass production as a tri-layer acoustic polyvinyl butyral interlayer supplied by Eastman Chemical Company. The QS31 grade is identified by a nominal thickness of 0.76 mm and a transparent sheet construction in which two PVB skins surround a softer acoustic core. The material is supplied in roll form for cutting on automatic interlayer lines and is used in automotive and architectural glazing where the interlayer must maintain glass retention after fracture, optical clarity, and measurable improvement in sound transmission loss. Automotive applications include windscreen and side-glass laminates certified under UN/ECE R43, FMVSS 205, or ANSI Z26.1; architectural applications are typically tested within laminated safety glass systems according to EN ISO 12543-2. The product is not a structural load-bearing interlayer, and open-edge glazing designs require separate edge-stability verification.

Acoustic damping in laminated glass arises from the constrained-layer effect between two glass plies. When the glass panels bend at the coincidence frequency, the interlayer is placed in shear. In a monolithic PVB interlayer, room-temperature damping is governed by the loss modulus of PVB itself; in Saflex QS31, the core introduces a lower-stiffness layer between two PVB skins, which increases shear strain in the core without removing the outer skins’ adhesion or moisture resistance. Laboratory characterisation of this effect is normally performed according to ISO 16940:2008, which measures mechanical impedance and allows calculation of the loss factor of glass–interlayer–glass test specimens. Full assembled glazing transmission loss is measured according to ISO 10140-2 and rated by ISO 717-1, or in North America by ASTM E90-09 and ASTM E413. Published product-specific loss-factor curves for Saflex QS31 are limited in public literature; therefore, project acoustic calculations should rely on supplier datasets or measured values from the selected glass configuration.

What Distinguishes Saflex QS31 From a Monolithic PVB Interlayer?

The first distinction is the approach to damping. A monolithic PVB interlayer is formulated for adhesion, moisture regulation, impact energy transfer, and optical quality; acoustic damping is a secondary effect. Saflex QS31 modifies that profile by inserting a middle layer that increases vibration decay around the coincidence dip, while the outer PVB layers preserve conventional PVB adhesion to glass and processing behaviour. The second distinction is thickness efficiency. A tri-layer sheet of 0.76 mm can replace a standard 0.76 mm monolithic PVB without altering the interlayer channel or glass build. This is significant in automotive glazing where the glass thickness budget is fixed. The third distinction concerns edge-seal interactions. Because the acoustic core is encapsulated between PVB skins, the product maintains the same general edge compatibility as PVB, although incompatible sealants can still extract plasticiser or produce haze at open edges. Published comparison data for QS31 against specific competitor tri-layer products is limited.

Compared with a conventional PVB monolayer of the same thickness, the principal trade-off is the reduced shear modulus of the acoustic core. This can require reassessment of post-breakage retention in glazing designs where the interlayer is expected to carry long-term tensile load after glass fracture. Compared with ionoplast structural interlayers, Saflex QS31 does not provide equivalent post-breakage stiffness at elevated temperatures and is not interchangeable in open-edge structural glass. Compared with EVA or PET-based laminated composites, PVB has lower moisture resistance and lower intrinsic resistance to prolonged exterior exposure; QS31 is therefore intended for encapsulated edge conditions in glazing pockets or frames.

Thermal and Pressure Conditions in a Production Autoclave Cycle

On a production laminating line, Saflex QS31 is handled in the same sequence as conventional PVB: roll staging, cut-to-size, layup in a clean room, de-airing, and autoclave bonding. The layup area is typically conditioned to 18–22°C and 20–35% RH. Moisture control is more important for acoustic PVB than for standard PVB because the acoustic core may be more sensitive to moisture-induced bubbles or reduced cross-layer adhesion if unprotected rolls are exposed to high humidity. If rolls have been stored outside controlled conditions or the ambience exceeds 60% RH, pre-drying should be considered. De-airing can be performed with vacuum bags, vacuum rings, or nipper rollers; for tri-layer structures, air entrainment between the core and skin is critical, and a short vacuum hold at 0.06–0.09 MPa is commonly used before autoclave. Autoclave bonding follows conventional PVB cycles: heat-up to 130–140°C, pressure 10–14 bar, and hold times of 30–60 minutes depending on glass area and loading density.

On high-volume automotive lines, cycle time is often determined by glass temperature rather than chamber elapsed time. Centre-glass temperature must remain above the PVB flow region long enough for bubble dissolution, but premature unloading at high temperature can leave edge bubbles. Controlled cooling is therefore part of the process window. Production experience on flat-laminating lines indicates that a cool-down rate of approximately 1°C/min below 70°C reduces thermally induced edge stress in large architectural panels. Incoming rolls should be logged for thickness profile, edge curl, and moisture, because batch-to-batch variance in roll storage can produce differences in autoclave yield even when chamber settings are unchanged.

The above table reflects general published ranges for multilayer acoustic PVB lamination. It is not a substitute for the Saflex QS31 product data sheet, because product-specific moisture limits and adhesion-controlled time–temperature curves may be narrower for a given sheet lot.

When Saflex QS31 Replaces Standard PVB in High-Rise Facade Glazing

In high-rise facade glazing, the acoustic interlayer is specified when the glass package must reduce exterior noise without increasing overall thickness. A common build may be 6 mm heat-strengthened glass / 0.76 mm QS31 / 6 mm heat-strengthened glass. In this configuration, the interlayer does not significantly change the static bending stiffness of the glass pair because the PVB thickness is small compared with the glass plies. The weighted sound reduction index of the assembly is determined by glass mass, cavity depth in an insulating glass unit, and interlayer damping. The QS31 core shifts the coincidence-dip loss factor, but the overall improvement is frequency-dependent. Published data for this specific configuration is limited, and laboratory measurements according to ISO 10140-2 should be generated for project-specific facade prints. Edge deletion of 2–4 mm is normally retained around the perimeter, but the exposed interlayer edge must not be in continuous contact with water or alcohol-based cleaning agents until the edge seal is fully cured.

For interior partitions and acoustic doors, QS31 is not a mass barrier but a damping layer. The interlayer is commonly used in asymmetric glass builds that separate the two glass coincidence frequencies. In such designs, the loss factor increase can reduce transmission in the 1600–4000 Hz region that governs speech annoyance and high-frequency urban noise. Acoustic inserts using QS31 in multi-cavity insulating glass units should be modelled with measured loss-factor data rather than generic PVB damping values, because the tri-layer core shifts temperature-dependent damping relative to monolithic PVB. On site, edge over-sealing with incompatible silicone or open unprotected edges can produce local haze at the interlayer edge; this does not normally affect the central vision area but is unacceptable for exposed-edge decorative glazing.

Moisture Uptake, Pre-Drying, and Edge-Seal Incompatibilities

PVB is hygroscopic. Rolls of Saflex QS31 should remain in original aluminium or polyethylene packaging until layup. Storage at 10–25°C and 20–35% RH is typical for controlled interlayer rooms, with a supplier-defined shelf life. Moisture content above 0.45% by weight can cause bubble formation during autoclave. If rolls are exposed to 60% RH or higher for more than a few hours, pre-drying at 30–40°C may be required; however, product-specific drying conditions must be obtained from the supplier for QS31, because local overheating can block or distort the acoustic core. Chemical incompatibilities include uncured amine-based silanes, certain acetoxy-cure silicones, and plasticizer-sensitive rubber gaskets; these can cause haze, edge staining, or loss of adhesion at the edge. Solvent wiping of the finished laminate edge should use only compatible aliphatic cleaners.

In laminated glass containing a tin-side glass surface, the PVB sheet should be laid against the tin side only after manufacturer guidance. Adhesion is tuned by both moisture content and glass surface chemistry; batch-to-batch tin-side oxidation state varies by float line, and this can shift pummel adhesion values. For laminated glass that will be bolted or structurally bonded, adhesion testing according to EN ISO 12543-4 or an equivalent supplier method is required before large production runs. If open-edge glass is used in a facade with a wet-glazed silicone joint, adhesion and edge stability must be tested with the specific sealant because plasticizer migration from PVB can reduce sealant bond strength.

Saflex QS31 Does Not Function as a Structural Interlayer; It Provides Damping Within a Laminated Composite.

In a laminated composite, load transfer after glass fracture is a function of interlayer modulus, adhesion, glass thickness, and edge support. The acoustic core in QS31 may have lower room-temperature modulus than standard PVB, which influences post-breakage deflection. For barrier or balustrade applications, the relevant standard is EN 12600 for impact safety or CPSC 16 CFR 1201 in the United States. The designer must verify by full-scale testing or validated calculation that the chosen glass build meets the required drop height and residual strength class; the presence of an acoustic core does not automatically confer a safety classification. For head-up display windshields, wedge correction and image ghosting are system-level optical requirements. QS31 is a flat interlayer unless specifically supplied as a wedged product; where wedge is required, a dedicated wedged PVB grade must be selected or the windshield geometry must be tested for projection overlay error.

Automotive acoustic glazing often pairs QS31 with thin outer glass plies of 2.1 mm or 2.3 mm to reduce mass while maintaining laminated safety performance. Road noise enters the cabin in a broad band, but the interlayer damping effect is most measurable where glass panel bending modes couple with the passenger compartment acoustic modes. In side-lite production, the interlayer is die-cut to the glazing outline, and the edge is typically set back from the glass edge to allow edge encapsulation. Production-scale failure modes include edge bubbles from insufficient de-airing, interlayer shrinkage from over-drying, and localised acoustic-core delamination from too-high autoclave temperature. Each batch should be qualified with a small-panel adhesion pummel test and a visual inspection under transmitted light before line ramp-up.