| HS Code | 573747 |
| Product Name | Kuraray VPK702-PVA Structural Fiber (Stiff Type) for Paper Making |
| Material | Polyvinyl Alcohol (PVA) |
| Fiber Category | Short-cut synthetic structural fiber |
| Stiffness Type | Stiff type, high flexural rigidity |
| Fiber Length | 2 to 3 mm available cut length |
| Fiber Fineness | Approximately 7 dtex |
| Fiber Cross Section | Round or high-stiffness compact cross section |
| Color | White |
| Density | 1.26 to 1.30 g/cm³ |
| Fibrillation Tendency | Low; non-fibrillating stiff fiber |
| Tensile Strength | High; typically 10 to 13 cN/dtex |
| Elongation At Break | Low; approximately 6 to 9% |
| Initial Modulus | High; typically 250 to 300 cN/dtex |
| Moisture Regain | Low; approximately 3% at 20°C and 65% RH |
| Chemical Resistance | Resistant to common organic solvents, oils, and dilute alkalis |
| Thermal Resistance | Stable under typical paper drying conditions |
As an accredited Kuraray VPK702-PVA Structural Fiber (Stiff Type) for Paper Making factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 20 kg net per multi-layer paper bag with inner polyethylene liner, palletized, shrink-wrapped, and protected for safe transport. |
| Container Loading (20′ FCL) | One 20-foot full container load of Kuraray VPK702-PVA Structural Fiber (Stiff Type) for Paper Making, packed on pallets. |
| Shipping | Kuraray VPK702-PVA Structural Fiber ships as dry, bale-packed rolls or cartons, sealed against moisture. Keep away from water, humidity, and direct sunlight during transport. Storage below 30°C recommended. Non-hazardous, but handle with care to prevent fiber breakage. Ensure proper labeling and ventilation. Avoid compression or stacking overload. |
| Storage | Store Kuraray VPK702-PVA Structural Fiber in its original, sealed packaging in a cool, dry, well-ventilated area away from direct sunlight, moisture, and ignition sources. Keep off the floor on pallets to prevent water damage, and segregate from oxidizing agents and strong acids. Maintain moderate humidity and temperature to preserve fiber stiffness and paper-making performance. |
| Shelf Life | Shelf life is at least two years when stored unopened in a cool, dry place away from direct sunlight. |
High-efficiency air filtration media based on borosilicate microglass develop tensile weakness at calipers below 0.4 mm unless a stiff, low-elongation reinforcing fibre is introduced at the wet end. Kuraray VPK702 stiff PVA staple is incorporated at 3.0–8.0 wt% of total furnish, replacing an equivalent mass of glass microfibre rather than cellulose, so that the furnish retains a bimodal fibre length distribution with glass median diameter 0.8–2.5 µm and a stiff PVA staple cut length of 4 mm or equivalent mill cut. Compliance for finished high-efficiency filters is governed by EN 1822-1:2019 class H14 and ISO 29463-5 for leak-free construction; media tensile is measured to ISO 1924-2, air permeance to ISO 5636-5, and thickness to ISO 534:2011. Processing on an inclined-wire wet-laid former uses headbox consistency 0.01–0.04 wt%, wire speed 50–120 m/min, pH 2.8–3.5, and an acrylic or phenolic binder add-on of 4–6 g/m² dry before through-air drying at 120–140°C. At addition levels below 3.0 wt%, the pleating line at 20 mm pleat depth shows elevated tip cracking; above 8.0 wt%, pressure drop at 5.3 cm/s face velocity rises at a faster incremental rate than burst strength, creating a line-specific processing window. Converted products include H14 terminal HEPA panels, mini-pleat cleanroom filters, and vacuum cleaner exhaust cartridges.
For Zn/MnO₂ primary cell separator paper, the structural layer must retain wet strength in 35–40 wt% KOH at 60°C while limiting fibre release that can bridge electrode gaps in cylindrical LR6 and button LR44 cells. VPK702 is dosed at 10–25 wt% against mercerised softwood pulp; at the lower bound it acts as a fibrillation suppressant, while at 25 wt% the dry tensile index under ISO 1924-2 is maintained in the range of 45–60 N·m/g after 168 h alkali immersion at 60°C. Compliance references include IEC 60086-5:2021 for primary battery safety, EU Regulation 2023/1542 Article 6 for substance restrictions in batteries, and REACH EC No 1907/2006 Annex V for polymer registration exemption status of polyvinyl alcohol. The downstream process uses a cylinder mould or inclined-wire wet-laid machine at basis weight 25–40 g/m², followed by thermomechanical calendering at roll surface temperature 160–180°C and nip pressure 100–150 kN/m to reach caliper 30–50 µm; calendering below 160°C leaves excessive pore-size scatter, while above 180°C may cause local film formation on the PVA fibre surface. Pore-size distribution data for VPK702 at 30 µm finished caliper is limited in public literature; pilot-scale cylinder mould validation is required before specification freeze. End products are separator papers for alkaline Zn/MnO₂ cylindrical and button cells.
In spin-on oil filter media, the dominant failure mode after hot-oil ageing is not tensile rupture but embrittlement of the phenolic-impregnated cellulose network, which sheds debris into the clean-oil side. VPK702 is added at 8–18 wt% of total fibre mass in the furnish, partially replacing bleached softwood kraft and leaving total synthetic fibre content below 40 wt% so that resin saturation remains uniform. Compliance tests follow ISO 4548-12 for steady-state filtration and retention capacity of full-flow lube oil filters, ISO 2941 for collapse resistance of the pleated element, and ISO 1924-2 for saturated media tensile after 72 h immersion in SAE 10W-30 oil at 120°C. The wet-laid Fourdrinier line runs at basis weight 130–160 g/m², headbox pH 5.5–7.0, and refiner specific edge load of 0.8–1.2 J/m. After papermaking, phenolic resin is applied at 20–25 wt% resin solids pick-up, cured through a tunnel dryer, and the media is corrugated at pleat heights of 20–50 mm and pleat density 8–12 pleats per 100 mm. Above 18 wt% VPK702, water removal on the wire becomes slower and the dry-line position moves downstream by 2–4 m on a typical 30 m forming table, requiring either speed reduction or additional vacuum boxes. Converted end products include spin-on lube oil filter elements, cartridge filters for heavy-duty diesel engines, and hydraulic return-line filters.
Flatback masking tape base paper produced with 5–12 wt% VPK702 substituted for bleached softwood kraft increases internal bond as measured by TAPPI T 569 and reduces fibre pick-out when saturated with SBR or acrylic latex at 40–60 wt% pick-up. Compliance for the converted tape is checked under ASTM D3652/D3652M-20 for tape thickness, ISO 29862:2018 for peel adhesion to steel, and ASTM D3759/D3759M for tensile strength and elongation of pressure-sensitive tape. The base paper is wet-laid on a Fourdrinier or gap former at basis weight 60–110 g/m²; after size press treatment with starch at 1.0–2.0 g/m² dry pick-up, the sheet is saturated on a two-roll saturator, then dried in a tunnel at 90–120°C. Stiff PVA fibre reduces machine-direction elongation, so crepe ratio must be kept below 1.20 when a flatback product is specified; above 12 wt% fibre addition, the base sheet displays a measurable reduction in saturation uniformity as detected by transmitted-light mottle. Converted end products include high-temperature flatback masking tape for automotive paint masking, surface-protection tape for powder coating, and silicone-splicing tape bases.
Wet tensile rather than dry tear governs runnability when alpha-cellulose overlay paper enters a melamine-formaldehyde impregnation line, because the web is rewetted to high saturation and then subjected to high-shear resination. VPK702 is added at 3–8 wt% of furnish, displacing high-alpha cellulose while preserving fibre purity for resin transparency. Compliance for finished high-pressure laminate surfaces is tested under ISO 4586-2 and EN 438-3:2016; base paper wet tensile is measured to ISO 3781, and transparency to resin is checked by laminating a single sheet over dark core stock. The downstream process starts on a low-consistency headbox at basis weight 20–45 g/m², then paper is wound at 7.0–9.0% moisture; impregnation with melamine-formaldehyde resin achieves 60–70 wt% resin content on fibre, followed by B-staging at 110–130°C and hot pressing at 140–160°C and 8–10 MPa. Above 8 wt% VPK702, resin wet-out can become locally slower because of the additional PVA fibre surface area, and optical clarity can shift such that the CIELAB delta L exceeds 1.0 against the resin-only control. End products are decorative overlay sheets for high-pressure laminates, flooring overlay papers, and low-pressure laminate paper systems.
Abrasive backing papers manufactured with stiff PVA fibre shift the dominant failure mode from fibre pull-out at the make-coat interface to cohesive resin failure during disc peeling, provided the fibre is fibrillated only lightly and not over-refined. VPK702 is charged at 5–15 wt% of the furnish alongside bleached softwood kraft and occasionally 10–20 wt% synthetic short-cut polyester. Backing tensile is measured to ISO 1924-2, bending stiffness to ISO 2493-1, and grit sizing to ISO 6344-1. The paper machine produces base stock at 110–160 g/m²; after wet-laying, the sheet is saturated with phenolic resin at 15–20 wt% dry pick-up and then coated on the abrasive side with a make coat, electrostatic grain projection, a size coat, and final cure at 110–130°C. Fibre addition above 15 wt% reduces conformability during disc conversion and increases the rejection rate on flexing machines designed for cellulose-backed stock, particularly when bending stiffness exceeds 180 mN at 15° bend angle under ISO 2493-1. Converted end products include fibre-backed abrasive sheets, roll abrasives for metal finishing, and quick-change discs for orbital sanders.
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The principal difference between VPK702 and polyester, polyamide, or polypropylene staple in wet-laid processing is surface wettability and the low-strain stress–strain curve. Hydrophobic synthetic staple tends to agglomerate in aqueous suspension unless pre-dispersed with nonionic surfactants and defoamers; it also tends to float in low-consistency chests and produce fiber bundles in the headbox. VPK702 has an equilibrium moisture regain of approximately 4–5% at 65% RH, which is lower than bleached kraft pulp but substantially higher than PET. This moisture affinity reduces flotation and allows direct addition into the pulper or machine chest when the cut length is below 6 mm and stock consistency is kept below 0.8%. At higher consistency, the fiber can form rope-like aggregates in the stock approach system if local agitation velocity drops below the suspension velocity. The following table reports representative fiber-class data compiled from technical literature; it is not a substitute for VPK702-specific certification.
| Property | Stiff PVA class (VPK702) | Soft PVA staple | PET staple | Aramid staple | Bleached softwood kraft |
|---|---|---|---|---|---|
| Density (g/cm³) | 1.26–1.30 | 1.26–1.30 | 1.38 | 1.44 | 1.50 |
| Tenacity (cN/dtex) | 7–10 | 6–8 | 4–7 | 19–27 | 3–5 |
| Initial modulus (cN/dtex) | 200–350 | 70–150 | 60–90 | 500–1000 | 50–100 |
| Elongation at break (%) | 6–10 | 10–20 | 15–30 | 2.5–4.5 | 3–8 |
| Moisture regain at 65% RH (%) | 4–5 | 4–5 | 0.4 | 3–5 | 7–9 |
Compared with a soft PVA staple, VPK702’s stiff designation corresponds to a higher initial modulus and lower elongation at break. That difference changes the sheet failure mode: a soft PVA fiber can yield locally under tensile loading and redistribute stress, while a stiff PVA fiber raises the tensile stiffness of the sheet until the fiber-matrix interface fails or the fiber breaks. Compared with aramid, VPK702 has lower modulus and lower thermal stability, but it is hydrophilic and requires less aggressive retention chemistry. Compared with bleached softwood kraft, VPK702 does not fibrillate or form hydrogen bonds to the same density, but it has higher tenacity and better wet strength retention. Differences from glass fiber are also significant: glass has higher modulus and lower elongation, but it is denser and more abrasive to forming fabrics and converting knives. VPK702 reduces the abrasion-related wire-life penalty, but it cannot match the stiffness of glass-reinforced sheet at equal addition. The choice between VPK702 and oxidized polyacrylonitrile, flax, or mineral fiber is governed by basis weight, caliper, air permeability, and the required wet strength.
Poly(vinyl alcohol) fiber is selected for wet-laid filter media and overlay papers where the sheet must retain mechanical integrity during heated calendering, resin impregnation, or thermal curing. VPK702 does not behave as a low-melting bonding fiber; it remains fibrous at temperatures where polyethylene or sheath-core polyester bonding fiber would collapse and flow. The upper continuous-use temperature of acetalized PVA fiber is bounded by oxidative degradation and discoloration rather than melting; the homopolymer glass transition is near 85°C, but wet-spun drawn fiber responds with a different thermomechanical curve. Decomposition begins near 220–240°C under air, and sheet discoloration can appear earlier if the furnish contains residual lignin, alum, or acid. In resin-bonded overlay paper, VPK702 is added to improve resistance to surface cracking during impregnation and to reduce edge tear on converting lines. The fiber is compatible with aqueous resin baths between pH 4.5 and 8.0, but prolonged immersion in water above 80°C can cause surface swelling and partial dissolution unless the fiber is highly acetalized. Drying above 150°C should be controlled for moisture and residence time because residual moisture plasticizes the PVA and can allow wet-web elongation before cure.
On production paper machines, VPK702 behaves as a non-fibrillating, low-anionic furnish component. It does not generate fines under low-consistency refining, but disk refiners can cut the staple if the fiber is introduced ahead of the refiner. Shear-lag estimates for a stiff PVA fiber with tenacity near 8 cN/dtex indicate that the critical fiber length in a moderately bonded cellulosic matrix is generally above 2 mm; cut lengths shorter than 2 mm therefore contribute less to tensile load transfer and act more like bulky filler. The preferred addition point is after refining, either in the machine chest or at the fan pump suction. At addition levels above 5 wt%, drainage can decline measurably because the synthetic fibers occupy void volume and restrain sheet consolidation; vacuum flatbox load or machine speed may need adjustment. Retention is controlled with cationic polyacrylamide at 200–500 g/t and microparticulate silica, adjusted to headbox charge. PVA fibers under typical papermaking zeta potentials of -20 mV to -30 mV do not strongly flocculate, so retention aid demand is lower than for unmodified aramid but higher than for cellulosic fines. Formation uniformity should be checked with TAPPI/ANSI T 205 sp-18 handsheets or ISO 5269-2:2019 laboratory sheets before machine trials. Inclined-wire formers for wet-laid nonwovens can accept longer cuts than fourdrinier machines because the forming length and drainage path differ; however, the same flocculation mechanisms apply.
Because VPK702 has a low anionic charge, cationic starch and cationic retention aids can adsorb onto the fiber surface. Charge demand measurements with a streaming current detector should be used to set retention-aid dosage after the fiber addition point, particularly when filler loading is high. In furnishes containing calcium carbonate, the synthetic fiber can reduce first-pass ash retention because it occupies interstitial network sites where filler would otherwise be retained. Industrial trials on fourdrinier machines have shown that VPK702 can accumulate in broke systems if the fiber is not dispersed before discharge; because it does not fibrillate, it can survive multiple repulping cycles and appear as discrete long-fiber fractions in recovered stock. This is an operational difference from low-melting bicomponent fibers that can soften in the dryer and agglomerate in broke loops.
In sheet testing, VPK702 primarily increases tensile index, stiffness, and folding endurance, but its effect on tear index is nonlinear. Cellulosic papers normally show a positive correlation between tensile index and internal fiber bonding up to a process-specific plateau; a stiff synthetic fiber can raise tensile stiffness while reducing local strain capacity at the fiber-matrix interface. At addition above 7–10 wt% in high-density sheets, the sheet may show a plateau or decline in internal bond strength as measured by ISO 16260:2016 because the synthetic staple interrupts cellulose-to-cellulose hydrogen bonding. The practical addition window is therefore narrow and furnish-dependent. Stiff PVA fiber should not be treated as a drop-in replacement for soft PVA fiber; recycled fiber furnishes with short fiber fractions may require additional cellulosic refining to maintain internal bonding at equal VPK702 addition. In abrasive paper base, stiff PVA fiber is used to resist dimensional change during resin saturation and to reduce edge tearing on converting lines; however, the final tradeoff is between tensile stiffness and burst/tear properties. Tensile index is measured by ISO 1924-2:2008, tear index by ISO 1974:2012, folding endurance by ISO 5626:1993, and air permeability by ISO 5636-3:2013. In high-speed converting, the low-strain modulus of the sheet is often more relevant than ultimate strength because register control and web steering respond to the initial elastic modulus.
Operational boundaries include moisture storage, chemical compatibility, and food-contact status. Opened bales should be stored below 65% RH; at relative humidity above 70%, moisture absorption can produce fiber clumping and uneven feed at the cutter. If the fiber surface is visibly damp, the material should be reconditioned before use. VPK702 is insoluble in cold water, but prolonged exposure to water above 80°C can produce surface swelling and partial dissolution depending on acetalization. Strong oxidizing agents such as alkaline hypochlorite above pH 9 and temperatures above 50°C can degrade fiber tenacity. The fiber should not be combined with concentrated sulfuric acid or strong nitric acid; aqueous acidic conditions below pH 2 can slowly hydrolyze acetal groups. There is no direct food-contact claim available for VPK702 without a grade-specific migration test under EU 1935/2004 or FDA 21 CFR conditions; food-contact paper applications should be confirmed against the supplier’s compliance certificate and the applicable regulation, such as 21 CFR 176.170 or 21 CFR 176.180. Published data for VPK702 in specific food-contact configurations is limited.
