Kuraray VPB203-PVA Structural Fiber for Paper Making

Kuraray VPB203 PVA structural fibre is metered into wet-laid filtration base stock at addition rates between 5 wt% and 20 wt% on bone-dry furnish. The fibre cut length is held at 3 mm to 6 mm; at these dimensions, fibre count per gram exceeds 3,000 at 1.0 dtex, which increases bondable surface area without forming the roping defects observed when longer synthetic staple is processed on inclined wire formers. Dispersion is carried out in a low-shear pulper at 2.0% to 2.5% consistency with a nonionic wetting agent dose of 0.05 g/L to 0.20 g/L added before furnish blending. After dilution to headbox consistency of 0.4 g/L to 1.0 g/L, the stock is formed on an inclined wire at a wire speed differential not exceeding ±5% relative to jet speed. Wet-end pH is buffered between 6.0 and 7.5, with zeta potential controlled to −15 mV to −25 mV using a dual retention system of cationic polyacrylamide at 0.02% to 0.06% dry pulp and colloidal silica or bentonite at 0.1% to 0.3%. Drainage is monitored by ISO 5267-1; stock freeness is maintained between 22 °SR and 40 °SR because freeness above 40 °SR produces sheets that fail converter pressure-drop specifications under ISO 5636-3. After formation, the web is dried on a through-air dryer at 120 °C to 145 °C and densified on a soft-nip calender at 70 kN/m to 90 kN/m line load. Dry tensile and wet tensile are measured according to ISO 1924-2 and ISO 3781, respectively; the tensile response is furnish-dependent, and mill control is based on normalized tensile energy absorption rather than absolute fibre-loaded claims. Wet tensile retention remains between 35% and 55% after 15 min immersion in deionised water at 23 °C in comparative wet-lay trials. Foam generation in the white-water circuit is controlled by metering a silicone-free defoamer at 0.05 wt% to 0.10 wt% on stock solids; defoamer addition above 0.30 wt% can depress wet tensile by reducing fibre-to-fibre hydrogen bonding. The main process conflict is that increasing VPB203 content above 20 wt% lowers first-pass retention and extends drainage time, particularly on suction breast roll formers where the sheet leaves the wire at 12% to 18% solids before pressing.

Why Does Heat-Seal Tea Bag Base Paper Demand a Binder Fibre with Both Hydraulic Dispersibility and Controlled Softening?

Tea bag base paper converted on high-speed form-fill-seal machines requires a synthetic fibre that disperses without entangled nodules at 16 g/m² to 24 g/m² basis weights and still forms restrained-pressure bond sites when jaw temperature is cycled at 170 °C to 200 °C. VPB203 PVA staple is refined into the furnish at 8 wt% to 15 wt% alongside long-fibre abaca and bleached softwood kraft; the synthetic component is first pre-dispersed in a side tank at 1.0% consistency for 10 min to 15 min using a low-speed agitator operating below 3 m/s tip speed. The furnish is formed on a suction breast roll machine at 0.3 g/L to 0.7 g/L headbox solids, with wet-end pH held at 5.5 to 6.5 to suppress alkali-driven fibre swelling. After drying to 4% to 6% equilibrium moisture, the sheet is calendered to a Bendtsen air permeance between 800 mL/min and 1,400 mL/min under ISO 5636-3. Heat-seal activation is tested on a laboratory jaw sealer at 180 °C, 0.4 MPa, and 0.5 s dwell; seal strength is recorded by separating the sealed seam on a tensile tester according to ISO 1924-2, with failure required to occur in the base sheet rather than at the seam. Published data for this specific configuration is limited, but converter trials indicate that jaw temperature overshoot beyond 220 °C produces local discoloration and seal embrittlement because polyvinyl alcohol begins to degrade under restrained pressure. The thermal processing window is therefore held to ±5 °C across the jaw width, and infrared thermography is used on production lines to map jaw-temperature uniformity. The main process conflict is between high porosity for infusion and tight seam formation: over-refining to improve sheet formation closes the pore structure, while under-refining produces weak seams and loose fibre ends.

Battery separator base stocks respond to polar fibre surfaces by increasing electrolyte retention.

In alkaline battery separator papers, Kuraray VPB203 PVA fibre is added at 5 wt% to 15 wt% to a furnish of low-lignin eucalyptus, lyocell, and mercerized kraft. The polar hydroxyl surface of the polyvinyl alcohol fibre increases wicking of 35 wt% to 45 wt% potassium hydroxide electrolyte, measured gravimetrically after 24 h immersion at 23 °C and compared with capillary rise under ISO 8787. Sheet basis weight is controlled at 50 g/m² to 80 g/m², with thickness between 60 µm and 110 µm and air resistance measured by TAPPI T 460 from 0.5 s/100 mL to 2.0 s/100 mL. The PVA staple is cut to 3 mm to avoid through-thickness fibre channels that reduce isotropic electrolyte distribution. Polyvinyl alcohol fibre does not hydrolyse in strong alkali at ambient to 60 °C, distinguishing it from polyester fibre, which undergoes surface saponification under prolonged potassium hydroxide exposure. Chemical resistance screening follows ISO 175 principles adapted for sheet stock, with fibre mass loss below 2% after 72 h in 40 wt% potassium hydroxide at 60 °C. Fibre distribution on a cylinder paper machine at 0.2% to 0.5% headbox consistency is sensitive to stock temperature; below 15 °C, retention aid adsorption on the synthetic fibre surface decreases, and first-pass retention falls below 85%. The absence of a single ISO method for alkaline battery separator absorbency means laboratory control charts must specify immersion time, temperature, and potassium hydroxide concentration, with the in-house method correlated to ISO 8787 for paper and board absorption.

Kuraray VPB203 PVA fibre is incorporated into security paper furnish at 10 wt% to 30 wt% to raise fold endurance and resistance to tear initiation in banknote and identification substrates. The base sheet commonly comprises cotton linters, flax, and bleached softwood kraft refined at low specific edge load to preserve fibre length; synthetic staple of 4 mm to 6 mm is mixed into the beater chest before cylinder mould formation. Fold endurance is measured under ISO 5626 with a 9.8 N load; adding 20 wt% synthetic fibre increases double folds from a virgin cotton-linter baseline in the range of 800 to 1,500 double folds up to values above 2,500 double folds in dry conditions, although published data for this specific configuration is limited and machine-direction differences of 10% to 20% must be considered. Tear resistance, assessed by ISO 1974, is less influenced by the PVA fibre than by the long-fibre flax furnish; however, wet tensile retention measured under ISO 3781 remains above 40% because the PVA fibre does not lose dimensional stability when re-wetted, whereas oxidatively bleached cotton may lose 15% to 25% of dry tensile after wetting. In security papers, printability and watermark contrast are critical; the synthetic fibre can reduce transparency and create local variations in caliper if fibre count exceeds 30 wt%. Converter mills therefore run a double-disc refiner at no-load recirculation rather than positive refining to avoid cutting the PVA staple, and the stock is passed through a low-frequency deflaker with 0.5 mm to 1.0 mm plate clearance.

When VPB203 Fibre Is Carried into Release Base Paper for Solvent-Free Silicone Coating

Release base paper used for silicone-coated labels and tapes requires a closed, densified surface that limits platinum-catalysed silicone penetration; addition of VPB203 PVA structural fibre is held to 3 wt% to 8 wt% because the fibre surface hydroxyl groups raise Cobb water absorption and can alter surface polarity, leading to coating anchorage loss at fibre-rich zones. Base stock is produced with a furnish of bleached hardwood and softwood kraft refined to 35 °SR to 45 °SR, then surface-sized with oxidized starch or polyvinyl alcohol-based size at 0.5 g/m² to 1.5 g/m². The fibre is cut to 3 mm and added after refining to minimize fibrillation. Calendering is performed on a soft-nip calender or supercalender at 140 °C to 180 °C and 250 kN/m to 350 kN/m line load to lower Bendtsen roughness to 50 mL/min to 120 mL/min under ISO 8791-2. Cobb test under ISO 535 with 60 s contact time is controlled below 22 g/m²; if Cobb exceeds 30 g/m², silicone cure speed decreases in converter trials, and loop tack may be affected when measured by AFERA 5004. Published data for this specific configuration is limited because catalyst demand is highly dependent on silicone chemistry and platinum concentration; bath life is monitored by gel time measurements at 25 °C and 50% RH. When polyvinyl alcohol surface size is used alongside VPB203 fibre, the combined hydroxyl site density increases and the fibre addition is kept at 3 wt% to 5 wt% to avoid excessive Cobb variability.

For moulded pulp food-contact containers, VPB203 PVA fibre is blended into bagasse, recycled bleached kraft, or unbleached softwood pulp at 5 wt% to 15 wt% before vacuum forming on porous wire moulds. The fibre cut length is 3 mm to 5 mm; staple above 6 mm reduces screen coverage and can leave visible fibre tufts on tray surfaces after hot-press drying. The furnish is prepared at 1.5% to 2.0% consistency, diluted to 0.3% to 0.5% before forming, and then transferred to a vacuum mould where −0.06 MPa to −0.08 MPa vacuum pressure removes water. Wet preforms are pressed in heated matched metal tools at 180 °C to 210 °C and 10 MPa to 20 MPa surface pressure for 15 s to 60 s, during which VPB203 thermoforms and bonds adjacent cellulosic fibres, increasing dry tensile and edge crush resistance. Dry tensile testing follows ISO 1924-2; edgewise crush follows ISO 12192 adapted for moulded specimens.

Operational boundary: if drying temperature exceeds 220 °C, PVA fibre begins to yellow and may generate volatile aldehydes; therefore drying tunnels are zoned with the final stage held below 210 °C and residual moisture at 4% to 6% before discharge.