Butvar B-98

Wash Primer Chemistry for Grit-Blasted Steel and Chromate Conversion Aluminum

In two-component wash primers for structural steel and aluminium, Butvar B-98 functions as the carrier resin that entrains zinc tetroxychromate and phosphoric acid prior to overcoating with epoxy or polyurethane. Part A places the PVB content at 7.5 wt% to 9.0 wt% in a solvent blend of isopropyl alcohol, n-butanol, and toluene. The mixed primer contains phosphoric acid in the range of 3.0 wt% to 4.0 wt%, supplied as Part B. Above 4.0 wt% acid, ambient cure causes rapid acetal hydrolysis at the PVB chain, reducing film toughness and topcoat adhesion. Spray application on abrasive-blasted steel with a surface profile of 25 µm to 75 µm per ISO 8503-2 is performed with HVLP equipment at 2.5 bar to 3.0 bar atomising pressure. Wet film build is controlled to yield a dry film thickness of 8 µm to 15 µm. Above 15 µm, the zinc tetroxychromate loading creates a friable, non-adhesive interlayer. Viscosity of the mixed primer at 25 °C is typically 15 s to 25 s on a Ford #4 cup, and pot life on the shop floor is limited to 4 h to 6 h at 25 °C. The mixed wash primer must be allowed to flash for 30 min before application of an amine-cured epoxy topcoat. Residual phosphoric acid otherwise neutralises the amine catalyst and produces amine phosphate salts at the interface. For aluminium substrates, a chromate conversion coat per ISO 10546 is recommended. Untreated mill-finish aluminium produces variable adhesion. Storage of Part A above 30 °C accelerates butyral depolymerisation. A viscosity drift greater than 10% compared with fresh material is batch-rejection grounds.

Slot-die coating of barium titanate-based green sheet for X7R multilayer ceramic capacitors uses Butvar B-98 as the high-molecular-weight binder that retains green strength during lamination and punching. The ceramic slurry is prepared by dispersing barium titanate powder in a 60:40 toluene-to-ethanol azeotrope with a phosphate ester dispersant at 0.5 wt% to 1.0 wt% of ceramic mass. Butvar B-98 is added at a binder-to-ceramic ratio of 6 wt% to 12 wt% on dry powder mass, typically with butyl benzyl phthalate at 2 wt% to 5 wt% of binder solids. Ball milling proceeds for 18 h to 24 h in a zirconia-lined vessel with 3 mm to 5 mm yttria-stabilised zirconia media at 40 rpm to 60 rpm. Casting viscosity is held between 1000 cP and 5000 cP at 25 °C using a Brookfield RV spindle #6 at 20 rpm. If the slurry exceeds 5000 cP, solvent-rich skins form on the tape surface and entrapped air creates pinholes during doctor-blade casting. Tape is cast through a doctor blade gap of 50 µm to 250 µm onto a silicone-coated polyester carrier film at 0.5 m/min to 2.0 m/min, followed by three-zone drying at 60 °C, 70 °C, and 80 °C. Green tensile strength of the dried tape measured per an adaptation of ASTM D638-14 commonly falls in the range of 1.5 MPa to 4.0 MPa at 0.2 mm thickness. Layer lamination is carried out at 60 °C to 80 °C and 10 MPa to 30 MPa for 2 min to 5 min. Binder burnout in a continuous tunnel furnace is ramped from 250 °C to 450 °C in air at 1 °C/min to 3 °C/min. Residual carbon after burnout must remain below 0.1 wt% to prevent dielectric loss increases. A shift above 10% in Brookfield reading at fixed solids is treated as an incoming QC rejection. Zinc stearate lubricants and high-acid-value dispersants must be excluded because acid catalysis of the PVB acetal bond causes viscosity drift during milling beyond 24 h.

What Solvent Release Profile Governs High-Solids Gravure Ink Transfer?

High-solids surface-printing inks for treated polypropylene and polyester films use Butvar B-98 as a polar co-binder with nitrocellulose and polyamide. The PVB fraction in the dried ink film is typically 8 wt% to 12 wt%, while nitrocellulose is held at 20 wt% to 30 wt% and polyamide at 10 wt% to 15 wt%. The solvent blend for press-ready ink is composed of ethanol, ethyl acetate, and isopropyl alcohol in ratios adjusted to a press viscosity of 18 s to 25 s on a Zahn #3 cup at 25 °C. Gravure cylinders are laser-engraved to 60 lines/cm to 80 lines/cm with cell depths from 20 µm to 40 µm, and the press is run at 150 m/min to 300 m/min. Between-colour dryers exhaust at 50 °C to 70 °C. Residual solvent in the printed film should remain below 10 mg/m² when measured per ISO 11890-2. Adhesion to corona-treated BOPP requires a surface energy of at least 38 dyn/cm per ASTM D2578-17. Below this level, tape adhesion per ASTM D3359-09 drops under 4B. Blocking resistance of printed reels is measured per ASTM D4946-89. B-98-rich formulations can block above 35 °C unless a nitrocellulose excess is maintained. High ambient humidity above 80% RH in the press hall increases moisture absorption in the PVB phase and raises viscosity at fixed solvent addition, producing print mottle. Production QC limits retained ethanol by gas chromatography rather than gravimetric loss-on-drying. The retained ethanol threshold is set at 5 mg/m² for non-contact printed films. PVB forms strong hydrogen bonds with alcohols, so gravimetric results understate actual retention.

Cobalt-modified iron oxide dispersions for high-durability magnetic tape backings are compounded with Butvar B-98 at 8 wt% to 15 wt% of total solids as the primary thermoplastic binder. The pigment is first predispersed in a solvent blend of tetrahydrofuran, methyl ethyl ketone, and cyclohexanone using a phosphate ester wetting agent. Butvar B-98 is added before the batch is milled in a horizontal bead mill charged with 0.8 mm to 1.2 mm yttria-stabilised zirconia media at a chamber fill of 80% to 85%. Mill residence time runs from 6 h to 24 h depending on pigment surface area. Final dispersion viscosity at 25 °C is held at 500 cP to 2000 cP at 100 s⁻¹. The dispersion is coated onto 12 µm to 25 µm biaxially oriented polyester film by reverse gravure or slot-die at web speeds of 100 m/min to 300 m/min. A solenoid field of 100 mT to 200 mT orients the acicular particles in the wet coating before the first dryer zone. Steel/steel calendering follows at 80 °C to 100 °C and nip pressure of 200 kN/m to 300 kN/m, densifying the magnetic layer and reducing surface roughness to below 30 nm Ra as measured by optical profilometry. Abrasion resistance is verified on a Sutherland rub tester per ASTM D5264-98 against a reference head material. Published data for B-98-specific head wear rates is limited, but production records report improved cohesion over lower-molecular-weight Butvar grades. Amine-based dispersants must be excluded because residual amines attack the PVB acetal linkages during long-term tape storage. Humidity above 60% RH during winding can create sticking between adjacent tape layers. Tapes are therefore wound at 45% RH to 55% RH and 21 °C to 24 °C.

Controlling Lamination Cycle Time on Phenolic Honeycomb with Solvent-Cast Butvar B-98 Films

For aircraft interior sandwich panels, solvent-cast adhesive films based on Butvar B-98 laminate aluminium skins to phenolic-impregnated aramid honeycomb. The resin is dissolved at 20 wt% to 25 wt% solids in a methyl ethyl ketone/ethanol blend, doctored onto a fluoropolymer release liner, and dried to a film thickness of 25 µm to 75 µm. Lamination is performed in a multi-opening platen press at 140 °C to 160 °C under 0.5 MPa to 1.0 MPa for 20 min to 40 min. The high molecular weight of B-98 provides low cold flow during storage. Films remain dimensionally stable below 30 °C. Dry B-98 exhibits a glass transition near 72 °C. Absorbed water plasticises the film and lowers the effective glass transition below the lamination temperature. Lap shear strength on chromic-acid-etched aluminium per ASTM D1002-10 typically falls between 10 MPa and 15 MPa for unmodified B-98 films. Floating roller peel per ASTM D3167-10 shows cohesive failure within the PVB layer when moisture is excluded. Pre-drying of the adhesive film at 60 °C for 2 h is required if storage RH has exceeded 60%. Phenolic resole resins may be co-solvated at 5 wt% to 15 wt% on solids to improve elevated-temperature creep resistance. Amine-catalysed phenolic grades must be excluded because brown discolouration develops during pressing. Panel finishing requires a 24 h post-cure at 25 °C before dimensional inspection.

When Crosslinkable Butvar B-98 Blends Are Baked Below 170°C

When applied by three-roll coater on hot-dip galvanised coil, Butvar B-98 can be blended at 10 wt% to 25 wt% of binder solids with a methylated melamine-formaldehyde crosslinker. Peak metal temperature is maintained at 150 °C to 170 °C for 30 s to 60 s, enabling hydroxyl crosslinking without decomposing the PVB backbone. Flexibility after forming is checked by T-bend per ASTM D4145-10. Cure level is verified by methyl ethyl ketone double rubs per ASTM D4752-15. Fewer than 50 rubs signals incomplete crosslinking. The operating boundary is strict. Above 180 °C peak metal temperature, yellowing from PVB degradation accelerates.

During high-shear compounding of carbonyl iron powder for metal injection molding feedstocks, Butvar B-98 is added at 3 wt% to 6 wt% of feedstock mass as a backbone binder alongside a polyacetal primary binder. Compounding is performed on a co-rotating twin-screw extruder with an L/D ratio of 25:1 at a barrel temperature profile of 160 °C to 190 °C. The PVB phase retards particle-binder separation during injection moulding and provides green-machinable strength before debinding. Solvent debinding in an acetone bath at 45 °C to 50 °C removes the primary binder, while subsequent thermal debinding to 450 °C in flowing nitrogen eliminates the PVB backbone. Residual carbon must remain below 0.05 wt% for sintered steel parts. Batch variation in Butvar B-98 hydroxyl content alters solvent debinding rate. Incoming lots are therefore checked by gel permeation chromatography against a certified reference chromatogram before compounding.