Avicor 7305

Avicor 7305 is an aromatic polyester polyol supplied with a nominal hydroxyl number of 300–330 mg KOH/g when measured under ASTM D4274 or ISO 14900, an acid number not exceeding 2.0 mg KOH/g under ASTM D4662, and a water content not exceeding 0.10% under ASTM D4672. Dynamic viscosity at 25 °C is 2,700–3,500 mPa·s measured under ASTM D4878 or ISO 3219. The downstream processing windows in this section are constrained by those values; batch-to-batch movement outside the stated hydroxyl number interval alters isocyanate demand, and viscosity drift above 4,000 mPa·s requires static mixer and pump speed correction on production equipment.

Why does continuous double-belt lamination impose a viscosity and reactivity boundary on aromatic polyester polyols?

In continuous double-belt lamination of polyisocyanurate boardstock, Avicor 7305 is metered as the hydroxyl-bearing component against a polymeric MDI component containing 30.5–31.5% NCO at an isocyanate index of 250–260. The polyol blend is held at 20–27 °C; a lower temperature increases viscosity toward 4,000 mPa·s and produces pump cavitation, while a higher temperature shortens cream time. High-pressure mixheads operating at 15–25 MPa homogenize the phases within 0.2–0.8 s, and the reacting mixture is deposited between aluminium foil, bitumen fleece, or glass-fibre facers at 18–25 kg/min per 1.2 m line width. At the specified index, core density after rise is 33–42 kg/m³ under EN 1602 or ASTM D1622. Thermal conductivity after 180 d at 23 °C and 50% RH is 0.020–0.024 W/(m·K) under EN 12667 or ASTM C518. Fire classification under EN 13501-1 or ASTM E84 is assembly-dependent; the aromatic polyester promotes char formation but the final rating is controlled by facer composition, panel thickness, and flame-retardant loading. Dimensional stability from −20 °C to +75 °C and up to 90% RH is evaluated under EN 1604, with linear change normally below 1.0% after 24 h cure. Preheating the B-side to 30 °C lowers cream time from approximately 18 s to 12 s; above 40 °C, gelation inside the mixhead becomes probable when line speed falls below 4 m/min. Published full-scale line data for this specific polyester in continuous lamination is limited, but the pressure, density, and thermal ranges correspond to conventional PIR boardstock production conditions.

Spray-applied rigid foam operations in commercial roofing require a mixed B-side viscosity below 800 mPa·s at 40 °C; therefore Avicor 7305 is diluted with a low-viscosity aromatic polyester or reactive diluent before the jobsite reactor is charged. In truck-mounted systems such as Graco HFR or PMC PH-1000, the A-side is a solvent-free polymeric MDI containing 30.5–31.5% NCO, while the B-side contains Avicor 7305 at 30–60 wt%, tris(1-chloro-2-propyl) phosphate, a potassium octoate catalyst, polyether polyol, and a silicone foam stabilizer. Substrate temperature is kept above 50 °C and relative humidity below 50% to prevent condensation on the steel deck. Spraying at 110–150 bar mix pressure yields foam with core density 38–46 kg/m³ under ASTM D1622. Compressive strength at 10% deflection is 180–260 kPa under ASTM D1621, and closed-cell content is 92–97% under ASTM D6226 or ISO 4590. Dimensional stability at −30 °C, +80 °C, and 70% RH is controlled to less than 1.0% linear change under ASTM D2126. The aromatic polyester polyol shortens tack-free time to 15–25 s at 20 °C, but spray passes thicker than 50 mm generate internal exotherm above 150 °C; published equipment-bulletin guidance for high-pressure spray rigs warns of scorch and cell rupture at the interface under these conditions. The same limitation applies below 5 °C substrate temperature, where adhesion to primed steel falls below 0.2 MPa in pull-off tests under ISO 4624.

Structural bonding in transportation and panel lamination demands controlled acid number and moisture content.

Two-component polyurethane adhesives built with Avicor 7305 are processed through gear pumps and static mixers at a mixing ratio of 100:18 to 100:22 against a polymeric MDI prepolymer having 16.0% NCO. Before compounding, the polyester is dried to water <0.05% under vacuum at 80–90 °C for 2–4 h; residual water above 0.10% causes carbon dioxide porosity in the bondline and reduces lap shear on non-porous substrates. A filler package of 20–35 phr barium sulfate and 2–4 phr fumed silica yields a mixed viscosity of 20,000–40,000 mPa·s at 25 °C measured under ISO 3219. Pot life on galvanized steel at 25 °C/50% RH is 12–18 min. Lap shear strength on 1.6 mm cold-rolled steel after 7 d at 23 °C is 12–16 MPa under EN 1465 or ISO 4587. Water immersion at 23 °C for 14 d reduces lap shear by 15–25%, while adhesion to mineral wool facings in EN 14509-compliant sandwich panels is conditioned on a cured adhesive layer thickness of 0.2–0.6 mm. An acid number above 2.0 mg KOH/g consumes amine catalyst and retards surface cure at 23 °C/50% RH, lengthening through-cure from 24 h to more than 48 h. To avoid this, the formulator adds an acid scavenger at 0.3–0.5 phr and monitors batch-to-batch acid number under ASTM D4662. Published data for this specific adhesive system is limited; the cited ranges are typical for aromatic polyester polyol two-component bonding in metal-to-insulation assemblies.

Typically, cast polyurethane elastomer processing with Avicor 7305 begins with vacuum degassing of the polyester at 80 °C and 10–20 mbar for 1–2 h to remove adsorbed water before the isocyanate prepolymer is added. In a representative 85 Shore A system, chain extension is performed with 1,4-butanediol, and the mixed system is poured into open aluminium molds preheated to 60–70 °C. Pot life at 50 °C is 6–9 min, after which viscosity rises beyond 100,000 mPa·s and degassing is no longer possible. Cure is completed at 100 °C for 16 h, followed by conditioning at 23 °C/50% RH for 7 d. Hardness determined on a 6 mm plaque is 85–90 Shore A under ISO 48-4 or ASTM D2240. Tensile strength is 20–25 MPa and elongation at break is 350–450% when tested at 500 mm/min under ISO 37 or ASTM D412. Abrasion loss under ISO 4649-A is 35–50 mg at 10 N. The processing window is narrow: adding 1,4-butanediol more than 1.0 phr above the stoichiometric endpoint lowers gel time below 3 min and drives hardness above 95 Shore A; reducing chain extender by 1.0 phr leaves surface tack at demold, requiring demold delay beyond 120 min. Vacuum loss during degassing produces gas bubbles counted under a 10x microscope on a cut section; more than 10 bubbles/cm² larger than 0.2 mm is treated as reject-grade in hydraulic seal prototypes under normal factory inspection criteria.

When high-solids anti-corrosion primers are formulated with aromatic polyester polyols, pot life and pigment-wetting become the controlling variables.

At 70–80% volume solids, high-solids polyurethane primers based on Avicor 7305 are applied by airless or air-assisted spray equipment at 120–180 µm dry film thickness per coat. The aromatic polyester is combined with an aliphatic polyisocyanate hardener at a volume ratio of 4:1; the acid number of the polyol is held below 2.0 mg KOH/g to prevent flocculation of zinc phosphate and zinc-rich fillers. Mixed paint viscosity at 25 °C is 600–1,200 mPa·s under ISO 3219. Through-drying at 23 °C/50% RH is measured with a Beck-Koller recorder under ASTM D5895; surface-dry is reached in 45–60 min, and through-dry in 6–8 h. Pendulum hardness after 7 d is 110–135 s under ISO 1522. Salt spray resistance on abrasive-blasted steel per ISO 9227 is 1,000–1,500 h before scribe creep exceeds 2 mm at 80–100 µm dry film thickness. Cross-cut adhesion on oxidized steel after 240 h of 40 °C water immersion is rated 0–1 under ISO 2409 or ASTM D3359. The aromatic structure leads to QUV-A ΔE above 3 after 300 h under ASTM G154, so a two-coat system with an aliphatic acrylic topcoat is required for direct exterior exposure. Published data for this exact binder in high-solids primers is limited, but the weathering limitation is characteristic of aromatic polyester polyol films.

Pour-in-place appliance insulation uses Avicor 7305 as a component of the polyol blend, typically at 30–60 wt%, to raise the glass-transition temperature and reduce the polyurethane foam thermal conductivity under freezer storage conditions. The B-side is injected at 18–22 °C into a refrigerator cabinet preheated to 35–45 °C, and the foam rises against the liner and outer shell to a core density of 32–38 kg/m³ under ASTM D1622. Compressive strength required for drawer-loading is 120–160 kPa at 10% deformation under ASTM D1621. Thermal conductivity after 24 h at a mean temperature of 10 °C is 0.019–0.022 W/(m·K) under ASTM C518 or ISO 8301. Flow beyond 80 cm in a heated Brett mold is required before gelation; typical gel times at 35 °C are 45–60 s. Shelf-life moisture pickup in the B-side is limited to water <0.10% under ASTM D4672 to avoid liner blistering. Batch-to-batch variance in hydroxyl number greater than ±5 mg KOH/g changes the isocyanate demand enough to alter core density by more than 3 kg/m³, which is a critical threshold on production lines running a fixed polyol-to-isocyanate metering ratio.

Reactive hot-melt adhesive rheology with polyester polyol backbones and limited purge-stability windows

Heated tank melters running at 110–130 °C process reactive polyurethane hot-melt adhesives containing Avicor 7305 as the soft segment, where melt viscosity is 15,000–30,000 mPa·s under ISO 3219. The molten adhesive is applied at 100–200 g/m² through slot dies onto ABS/polycarbonate or wood substrates, and cure proceeds by moisture uptake at 25 °C/50% RH. Handling strength is reached in 3–5 d, and full cure is confirmed by FTIR-ATR when the NCO absorbance at 2,270 cm⁻¹ drops below detection after 7 d. T-peel strength on ABS/polycarbonate after 7 d is 6–10 N/mm under ISO 11339. In melter stability studies, viscosity rises by 20–30% over 8 h at 120 °C, and gelation occurs beyond 12 h unless the unit is nitrogen-blanketed and moisture ingress is below 100 ppm. This narrow purge-stability window is the main operational boundary: production lines using drum melters must schedule a complete purge every 8 h, and batch-to-batch variation in polyester acid number above 1.5 mg KOH/g accelerates the viscosity rise still further.

Discontinuous moulded rigid foam blocks are produced by mixing Avicor 7305 with polymeric MDI at an index of 180–220, filling a block mould at 25 °C, and demoulding after 20–30 min; this operation is well-established and requires no further elaboration.