Trosifol Natural UV

Trosifol® Natural UV is a polyvinyl butyral interlayer manufactured by Kuraray for laminated safety glass in which transmission of the natural ultraviolet component of daylight is a functional requirement rather than an unwanted side effect. The product is supplied in roll form in thickness increments of 0.38 mm, 0.76 mm, 1.14 mm, and 1.52 mm; the grade designation is the natural-UV PVB interlayer, and slit widths are converter-specified within the manufacturer’s roll width capability. Unlike standard PVB formulations that incorporate benzotriazole or benzophenone UV absorbers to screen the 300–380 nm band, Trosifol Natural UV is formulated without a broad-spectrum UV absorber package, so the finished laminate retains the penetration resistance, fracture-adhesion behaviour, and safety functions of a PVB interlayer while allowing a defined portion of the 280–400 nm region to pass through the glazing build. Material classification and film consistency are addressed under ISO 12543-2; adhesion and durability verification fall under ISO 12543-3 and ISO 12543-4.

The optical behaviour of the grade is configuration-specific and cannot be reduced to a single interlayer transmittance value. In standard PVB, the UV absorber package converts absorbed ultraviolet radiation to heat and imposes an effective cut-off near 380 nm. Trosifol Natural UV uses a stabiliser system that does not impose that cut-off. In a laminate assembled with low-iron float glass, the ultraviolet edge is therefore controlled primarily by the glass substrate, the glass–interlayer refractive-index stack, and any additional optical coating. UV transmittance is determined by EN 410:2011, which reports ultraviolet transmission weighted across the 280–380 nm band; visible transmittance and solar direct transmittance are reported under the same method. Because the interlayer is not the only UV-filtering element, a standalone film value has limited engineering use. Manufacturer-published spectral data for a 0.76 mm Natural UV build in clear float glass should be requested for the exact glass composition and thickness, because published data for all possible build combinations is limited.

The product is based on plasticised polyvinyl butyral resin and is manufactured by slot-die extrusion with in-line thickness gauging. The absence of a conventional broad-spectrum UV absorber does not mean unstabilised resin; the heat and light stabiliser system must protect the PVB backbone from degradation during extrusion, lamination, and service without blocking the desired UV transmission. For 0.76 mm gauge film, architectural interlayer thickness tolerance is commonly specified as ±0.02 mm. Tensile properties for PVB interlayers are commonly measured per ISO 527-3:2018; material consistency indicators for plasticised PVB typically include tensile strength above 20 MPa and elongation at break above 250%. Haze is measured per ASTM D1003-21 and is typically below 1.0% for virgin film. Moisture content is measured by coulometric Karl Fischer titration per ISO 15512:2019 and is controlled to 0.5 wt% maximum at layup. These film-level values are not structural design allowables; they are material consistency checks and do not replace laminate-level testing.

Adhesion to glass is influenced by wash-line pH, glass tin-side orientation, moisture content, and interlayer gauge. A pummel adhesion target of 3–7 is commonly used in PVB production control. A grade change from UV-blocking PVB to Trosifol Natural UV should not be treated as a drop-in substitution without a startup adhesion check on the production line, particularly if the wash line operates with high humidity or if the glass surface condition is not stable. The pummel test is a production control tool rather than an ISO method; the relevant durability verification remains ISO 12543-3, which includes boil, humidity, and radiation exposure. Laminators switching from UV-blocking grades should also inspect edge stability and laminate clarity because the stabiliser package differs even though the base PVB chemistry is similar.

What Separates the Natural UV Grade from UV-Blocking Interlayers?

The functional distinction is formulation rather than process. Standard PVB and Trosifol UV Protect are specified where ultraviolet screening is required, such as museum, archival, pharmaceutical, or UV-sensitive product glazing. In those grades, the UV absorber package reduces UV transmittance in the 300–380 nm band to values typically below <5% or <1% depending on grade and thickness. Trosifol Natural UV is the inverse specification: it retains safety-glazing properties while avoiding broad-spectrum UV absorption. It is therefore not interchangeable with UV-blocking interlayers in a bill of materials without deliberate revalidation of the spectral performance of the entire laminate.

Compared with Trosifol ES or ionoplast grades, Trosifol Natural UV has a lower tensile modulus and a more temperature-dependent shear transfer. It is not selected for structural stiffness or long-term post-breakage load capacity under sustained static load. Compared with Trosifol Sound Control, the natural-UV formulation is not optimised for acoustic loss factor; acoustic interlayers achieve higher damping through a specialised viscoelastic core. The selection among these grades is governed by the dominant performance attribute: ultraviolet transmittance for Natural UV, ultraviolet blocking for UV Protect, acoustic attenuation for Sound Control, and structural stiffness for ES or ionoplast grades. Trosifol Natural UV should not be specified where ultraviolet screening is the primary performance requirement.

On industrial flat-glass laminating lines, processing of Trosifol Natural UV follows the same unit operations as standard PVB: conditioned interlayer is laid up on washed glass, deaired by nip roller or vacuum bag, and then exposed to an autoclave cycle. The critical boundary values are moisture and temperature. Interlayer storage should be maintained at 18–22 °C and 20–40% relative humidity before layup; moisture content above 0.5 wt% can produce edge haze, air entrapment, or poor pummel adhesion after autoclave. Pre-drying is required when storage RH exceeds 60% or when roll edge protection has been compromised. A typical autoclave cycle used in production is 135 °C at 1.2 MPa for 60–120 min, but the exact profile must be tuned to glass thickness, autoclave loading density, and adhesion target. Because the UV absorber package differs from standard PVB, a grade change on a line should be accompanied by a short validation run measuring pummel adhesion and edge stability before full production batches are committed. This is not a replacement for safety testing; it is a process capability check using production-line test laminates.

Roll handling also affects production yield. Blocking of roll stock at temperatures above 30 °C can cause irreversible stretching during unwind; cold storage at 10–15 °C is beneficial before slitting when high ambient temperatures are present. The interleaf should be removed only at layup to prevent airborne contamination of the bonding surface. Contact with aggressive solvents, ketones, or amine-containing sealants should be avoided during fabrication because these can plasticise or haze the interlayer edge. In overhead glazing where edge condensation is more severe, edge sealing should use compatible silicone or polysulfide sealants after testing for plasticiser migration from the interlayer.

When Natural UV Transmission Governs the Laminated Build

Horticultural glazing is a primary application because standard PVB modifies light quality in the 280–400 nm band. Laminated safety glass with Trosifol Natural UV retains overhead impact safety while permitting UV-A and UV-B to reach plant canopies; the glass substrate still filters the shortest UV-B wavelengths depending on glass composition and thickness. In horticultural roof glazing, the interlayer is commonly used in overhead laminated glass within aluminium glazing profiles using EPDM gaskets. The build often comprises tempered low-iron glass of 4–6 mm with 0.76 mm or 1.14 mm Natural UV. Low-iron glass is specified to shift the ultraviolet absorption edge to a lower wavelength than standard soda-lime glass, increasing the UV-A transmitted through the laminate. Procurement should therefore specify both the glass substrate and the interlayer spectral data; the interlayer alone does not define the glazing spectrum.

Zoological and herpetological enclosure glazing is another case where laminated safety properties are required under EN 12600 or ANSI Z97.1 but ultraviolet transmittance is also a biological design parameter. For herpetological enclosures, the glazing team normally specifies the UV-B dose at the animal basking plane. Because UV-B is more sensitive to glass composition and laminate thickness than UV-A, the design calculation uses the spectral transmittance curve of the entire laminate, not the interlayer alone. The safety interlayer function permits large viewing panels that meet impact classification while providing UV transmittance that standard PVB would block. In these applications, the specifier should require a spectral transmittance report from the fabricator for the exact production build, including any low-emissivity or solar-control coating if present; a coating can reduce UV-B even if the interlayer does not.

Atria and solarium constructions may select the grade when designers require unfiltered daylight access while satisfying safety-glazing requirements. In these builds, solar direct transmittance and g-value are also relevant because the additional transmitted UV contributes to solar gain; both are determined under EN 410:2011. The glass substrate’s intrinsic UV edge is typically between 300 nm and 320 nm for clear float glass. Low-iron glass transmits further into the UV-A region, while coated glass may reduce the 280–400 nm band substantially. Because EN 410:2011 reports UV transmittance only across the weighted 280–380 nm band, specifiers with biological or photochemical requirements often request a full spectral transmittance curve from 280–450 nm in 5 nm increments rather than a single UV percentage.

Compliance Designations and Verification Matrix

The following test method and product standard designations are used to verify Trosifol Natural UV in laminated glass configurations. The applicable classification depends on the glass plies, interlayer thickness, and final assembly; a declaration of conformity cannot be made for an unspecified build.

The grade is not a UV-blocking product. Applications governed by conservation standards such as ISO 18916:2007 or photostability protocols such as ICH Q1B should use Trosifol UV Protect or another UV-filtering interlayer. The product is also not recommended for laminates incorporating UV-cured edge sealants or coatings unless the fabricator validates that the transmitted 315–400 nm band will not initiate unintended secondary reactions during lamination or service. In laminated glass with polycarbonate sheet, ultraviolet transmission may accelerate polycarbonate yellowing; compatibility must be verified by the polycarbonate supplier under the actual UV load.

For a zoological enclosure build using 6 mm tempered low-iron float glass with a 1.52 mm Trosifol Natural UV interlayer, the specification should require the fabricator to measure UV transmittance through the actual production laminate using a spectrophotometer calibrated for EN 410:2011 and to report both the 280–315 nm and 315–400 nm bands. The safety classification shall be confirmed on the identical build by EN 12600 or ANSI Z97.1 before installation, because a spectral performance measurement does not substitute for mechanical impact classification.