1.67 dtex (1.5D)×38/51mm Hydrophobic PP Staple Fiber for Hygiene Material

On a carded thermal-bond line running 38 mm 1.67 dtex hydrophobic PP staple at web masses between 12 g/m² and 22 g/m², the fiber’s average diameter of approximately 15.3 µm provides high fiber strand count per unit area, which supports low-basis-weight coverstock formation without the stiffness associated with coarser hygiene fibers. A standard diaper topsheet construction blends 80–90 wt% 1.67 dtex hydrophobic PP staple with 10–20 wt% PE/PP bicomponent staple; the bicomponent sheath softens at 130–135 °C and bonds the web while the PP core retains fiber integrity. Carding is performed on a flat card with worker/stripper roller geometry, and the web is then calender-bonded on an engraved roll with a bond area in the range of 14–19%. Roll surface temperature is maintained between 148 °C and 158 °C as measured by infrared pyrometer; operation below 144 °C produces insufficient bond strength, while sustained surface temperatures above 160 °C initiate film-like compaction of the fine PP filaments, reducing air permeability and drape. The specific cut length of 38 mm is preferred on compact card clothing because 51 mm stock increases cylinder loading at line speeds above 160 m/min. The hydrophobic spin finish is controlled to 0.10–0.25% by mass using solvent extraction; excessive finish above 0.30% can cause lapping on workers and contribute to calender roll contamination. Liquid handling for the finished coverstock is governed by EDANA WSP 70.3 strike-through and WSP 70.7 rewet; because the fiber is hydrophobic, a converter typically applies a durable hydrophilic treatment to the acquisition side before conversion into infant diaper topsheet, unless the coverstock is intended as a barrier layer. The nonwoven is evaluated for tensile behavior under ISO 9073-3, thickness under ISO 9073-2, and air permeability under ISO 9073-15; skin-contact biological safety is established under ISO 10993-5 and ISO 10993-10, with REACH EC 1907/2006 SVHC content maintained below 0.1%. Olefin-grade assurance under 21 CFR 177.1520(c) is applied only when the converter’s internal specification requires food-contact polymer certification.

What Limits Through-Air Bonding Uniformity in Thin Acquisition Layers?

When the same 1.67 dtex fiber is used in a through-air bonded acquisition layer, the primary constraint is the narrow difference between the bonding temperature of the carrier fiber and the softening range of the PP matrix. The PP fiber does not function as a through-air binder at standard oven settings; its melting point is roughly 160–168 °C, while through-air ovens for polyethylene-sheathed bicomponent fibers operate at 138–143 °C to prevent sheath polymer from dripping and blocking the forming wire. A typical ADL formulation therefore contains 20–40 wt% 1.67 dtex hydrophobic PP staple and 60–80 wt% PE/PP bicomponent binder fiber. At PP addition above 40 wt%, the fine fiber increases packing density and reduces the mean flow pore size, which can raise strike-through time under EDANA WSP 70.3 and reduce the ADL’s ability to accept multiple insults. Through-air bonding on a drum unit is controlled by hot air temperature, dwell time, and pressure drop. For a 45–65 g/m² acquisition web, production-scale settings commonly hold air temperature at 139–142 °C, dwell time at 2.5–4.0 s, and circulation fan pressure drop below 600 Pa to avoid compressing the web. If the line exceeds 145 °C, partial surface melting of the PP fibers creates fused filaments with reduced void volume; if the temperature falls below 135 °C, sheath bonding is incomplete and the web loses Z-direction strength. The finished ADL is tested for thickness retention under ISO 9073-2 and for wet resilience after repeated loading; the hydrophobic PP staple contributes wet collapse resistance because it does not swell in saline fluid. This layer is subsequently converted into adult incontinence brief acquisition layers, where the nonwoven must maintain a caliper of at least 0.8 mm under 2 kPa load to preserve void capacity.

In airlaid absorbent core production for ultra-thin feminine hygiene pads, 1.67 dtex 38 mm hydrophobic PP staple is metered through a bale opener and blended with bleached fluff pulp and superabsorbent polymer. A production formula in this segment may use 15–30 wt% PP staple, 50–70 wt% fluff pulp, and 10–25 wt% SAP, delivered through a hammermill and forming head at line speeds above 100 m/min. The PP staple resists aqueous swelling, and its hydrophobic surface prevents fiber-to-fiber hydrogen bonding with wet pulp, thereby limiting wet collapse after a third insult. In latex-bonded airlaid lines, the core is sprayed with 4–8 wt% ethylene-vinyl acetate or styrene-butadiene binder and dried in a staged oven; in thermal-bonded airlaid lines, 8–15 wt% bicomponent binder fiber is added to the blend and activated at 138–142 °C. Core density after embossing is typically held between 0.10 g/cm³ and 0.16 g/cm³, with embossing pressure below 1.5 MPa because higher pressure collapses the fine PP filaments and reduces acquisition rate. The hydrophobic PP staple also reduces dusting from the hammered pulp and supports edge integrity during core cutting and wrapping. For this airlaid configuration, published data for the exact interaction between 1.67 dtex PP and SAP in pressed cores is limited; converter trials are required to confirm the maximum PP loading before strike-through time exceeds the product specification. The finished core is tested under ISO 9073-2 for caliper, ISO 9073-4 for tear strength, and EDANA WSP 10.1 for absorbent capacity, with regulatory coverage under REACH EC 1907/2006 and OEKO-TEX Standard 100 product class I for skin contact.

Barrier Leg Cuff Nonwoven Laminate Process Window and Elastomeric Adhesion Limits

Hydrophobic 1.67 dtex staple is converted into a carded nonwoven at 14–22 g/m² for leg cuff substrates in adult pull-up diapers and briefs. The carded web is point-bonded through an engraved roll at 146–154 °C with a bond area of 18–24%; bonding above 24% reduces the softness required for skin contact, while bonding below 15% causes edge fraying during subsequent slitting. The nonwoven alone at 14–22 g/m² has limited hydrostatic resistance under ISO 811, so barrier performance is produced by adhesive lamination to a 12–18 µm polyethylene film or by using a heavier construction of 25–30 g/m². In production, slitting to widths of 40–70 mm requires edge tolerance within ±1.0 mm because elastic threads are applied by adhesive or ultrasonic bonding at the cuff edge; hydrophobic PP surface finish can reduce hot-melt adhesion if finish levels exceed 0.25%, so corona treatment at 38–42 mN/m surface energy is sometimes specified before lamination. The resulting leg cuff composite is tested for tensile elongation under ISO 9073-3, hydrostatic head under ISO 811, and peel adhesion of the elastic laminate under ASTM D1876. This application avoids the need for hydrophilic finishing and uses the hydrophobic fiber as a fluid-impermeable structural layer at the cuff perimeter.

A panty liner coverstock may be produced from 1.67 dtex 51 mm hydrophobic PP staple to combine softness with reduced visible wetting. The staple is opened, carded into a 20–25 g/m² web, and thermally bonded with a pattern calender at 147–153 °C; the 51 mm cut length delivers a more anisotropic web with higher machine-direction tensile at equal basis weight, which supports high-speed conversion into panty liners and ultra-thin feminine hygiene pads. Since the fiber remains hydrophobic, fluid penetration is initiated through a central acquisition strip or a post-applied surfactant zone rather than through the full coverstock. This zoned treatment limits lateral spreading and helps maintain a dry surface. The nonwoven is evaluated under ISO 9073-3 for tensile strength, EDANA WSP 70.3 for strike-through after surfactant application, and ISO 10993-5 for in vitro cytotoxicity when the manufacturer markets the coverstock as a medical hygiene substrate. For cosmetic or hygiene use, OEKO-TEX Standard 100 product class I requirements are commonly applied. The cut length tolerance is controlled by the staple producer; converters running 51 mm staple should confirm that the opener and card clothing settings are adjusted to prevent fiber wrap on the main cylinder at line speeds above 140 m/min.

When 51 mm Cut Length Is Selected for High-Speed Carding in Adult Incontinence Coverstock

If a converter specifies 51 mm 1.67 dtex hydrophobic PP staple for adult incontinence coverstock, the processing trade-off is dominated by carding dynamics and machine-direction tensile development. The longer cut length increases the number of fiber-to-fiber contact points along the filament axis, which raises card web cohesion after doffing. On industrial nonwoven cards with main cylinder speeds above 1,000 m/min, 51 mm PP can produce higher MD tensile at the same calender settings, but it also raises the risk of cylinder loading if the fiber finish is below 0.10% or if the card clothing is worn. The web is bonded at 148–156 °C with a bond area of 16–20%; tensile anisotropy under ISO 9073-3 typically shifts toward MD/CD ratios of 1.4–2.0, which favors conversion into adult briefs where machine-direction strength is required during elastic leg application. However, the same anisotropy can cause necking and width loss during adhesive lamination. Published data for this specific configuration is limited; trials should compare 38 mm and 51 mm stocks on the same card line before finalizing the purchased fiber specification. The finished coverstock is used as an acquisition-facing layer in adult incontinence pads and is evaluated for strike-through under EDANA WSP 70.3 and for rewet under WSP 70.7 after the application of a durable hydrophilic finish.