OEKO-TEX Certified Skin-Friendly PP Staple Fiber for Diapers & Sanitary Towels

In two-layer baby diaper topsheet manufacture on flat-wire carding lines, the fiber charge is typically a blend of 1.5–2.2 dtex hydrophilic PP staple fiber cut to 38–51 mm and 20–50 % PE/PP bicomponent fiber. The melt mass-flow rate of the PP staple fiber is normally held between 14 g/10 min and 25 g/10 min under ISO 1133-1:2022 condition M, keeping calender tack within the bonding window. The olefin feed is opened through two-stage fine-opening equipment, and the card web is directed into a thermal calender with engraved roll temperature maintained between 135 °C and 155 °C and nip linear pressure in the 60–110 N/mm range. Bond area is controlled at 16–22 % by roll engraving depth; lower bond area produces lint release and strike-through variability, while higher bond area raises bending stiffness above the target range measured by ASTM D5732-19 and increases film-like surface friction. The fiber finish system must remain durable hydrophilic and must not transfer to calender rolls. On high-speed lines above 200 m/min, spin finish residue above 0.20 wt% on fiber can deposit on roll shoulders and create card doffer wrap. The card web is observed to have basis-weight CV below 4.0 % when web drafting is minimised. The finished topsheet, usually 14–20 g/m², is evaluated for tensile strength according to ISO 9073-3:2023, strike-through time with 0.9 % saline via EDANA/INDA WSP 70.7, and rewet after load via EDANA/INDA WSP 70.8. OEKO-TEX Standard 100 certification is limited to product class I for infant skin contact; formaldehyde content is required below 16 mg/kg under ISO 14184-1:2011, and aqueous extract pH is maintained at 4.0–7.5 under ISO 3071:2020. Pre-drying is required when storage relative humidity exceeds 60 %, because surface moisture as low as 0.10 % can destabilise calender temperature at the nip and create point-bonding defects.

What Controls Rewet and Strike-through in Air-through Bonded Acquisition Layers?

Acquisition distribution layers for sanitary towels are converted as carded through-air bonded webs with basis weights from 25 g/m² to 50 g/m². The fiber recipe often combines 100 % high-crimp PP staple fiber with a sheath-core bicomponent at 30–70 % levels, but PP staple fiber with a low-melt sheath can be used alone when the through-air oven is operated under disciplined temperature control. The oven air temperature is held at 132–146 °C with residence time of 2.0–5.0 s. The processing window is narrow: below 130 °C, sheath polymer does not flow sufficiently, and the web loses thickness recovery under load; above 148 °C, surface fiber melt spots appear and liquid passage becomes uneven. Through-air drum open area should be maintained at 30–50 % and air velocity at 0.8–1.5 m/s to avoid fiber displacement. The ADL is measured for caliper under 0.5 kPa using ISO 9073-2:2021, for tensile strength using ISO 9073-3:2023, and for multiple-dose strikethrough with 5 mL synthetic menstrual fluid after 3 doses according to EDANA/INDA WSP 70.7. Rewet is controlled below 0.10 g for a 2.5 kg load after 3 min. Batch-to-batch variation in staple crimp recovery, when crimp retention falls below 70 %, reduces z-direction void volume and increases rewet. OEKO-TEX Standard 100 product class II compliance for direct skin contact is applied to finished sanitary towel ADL, with pH in aqueous extract within 4.0–7.5 and no detectable sensitizing dye classes from the fiber spin finish.

When SAP containment is specified for high-speed sanitary towel converting, a low-porosity carded thermal-bonded core wrap is produced from 1.3–1.7 dtex PP staple fiber at 38–40 mm cut length. The web is bonded on an engraved calender with roll temperature 138–150 °C, nip pressure 80–120 N/mm, and line speeds between 150 m/min and 250 m/min. Bond area is set at 17–22 %; below this range, SAP particles penetrate the wrap and contaminate production rolls, while above this range, the wrap becomes stiff and can crack at fold lines. Basis weight is tuned to 10–15 g/m². Pore size is evaluated by bubble point measurement; production wraps typically exhibit mean flow pore diameters between 25 µm and 40 µm. Tensile strength is verified according to ISO 9073-3:2023 with a minimum requirement of 2.5 N/5 cm in the cross direction, because core forming tension focuses stress in the transverse axis. SAP dusting is checked gravimetrically after 250 compression cycles; published data for this specific configuration is limited, so acceptance thresholds are line-specific rather than universal. Fiber lubricant selection is critical: ester-based lubricant migration can plasticize the thin calender-bond points and reduce seam strength by 10–15 % after 4 weeks at 40 °C storage. OEKO-TEX Standard 100 product class II is applied for sanitary towel core wrap direct skin contact, and the substrate must show no chloro-organic carrier residues.

Hydrophobic leg cuff barrier fabrics and their resistance to strike-through after 300 % elongation

Leg cuff barrier substrates are run on high-speed carding lines with basis weights of 15–25 g/m² and a non-hydrophilic spin finish. The PP staple fiber is typically 1.5–2.0 dtex and 38 mm cut length. Calender bonding at 140–155 °C creates a compact, film-like bond pattern for liquid holdout. The critical parameter is elongation recovery: the barrier must survive 300 % elongation during elastic attachment without pore rupture. Tensile elongation is measured with ISO 9073-3:2023, and dynamic elongational integrity is checked by repeated extension to 300 % for 50 cycles at 200 mm/min jaw speed. Fiber finish must remain hydrophobic; contact angle on the bonded fabric is required above 105° using ASTM D5946:2017. Surfactant contamination from shared air handling systems can reduce contact angle below 90° and trigger leg cuff leakage. The barrier fabric is supplied to diaper converting lines as slit rolls with width tolerance ±1.0 mm to prevent elastic thread exposure. OEKO-TEX Standard 100 product class I applies for infant diaper leg cuffs, and compliance includes formaldehyde below 16 mg/kg and absent APEO compounds.

When ultra-thin sanitary towel cover stock is converted at speeds above 800 m/min

Because thin webs absorb less heat at high line speed, ultra-thin cover stock below 18 g/m² requires fine denier PP staple fiber, typically 1.0–1.5 dtex, to maintain opacity and surface coverage. The fiber is cut to 38 mm and blended with 10–30 % bicomponent fiber for thermal bonding. Calender temperature is tightened to 135–150 °C; a ±3 °C variation across the roll face produces visible density bands. Line speeds above 800 m/min intensify doffing air turbulence, and web weight CV increases unless the card web is supported by suction transfer systems. The converted fabric is checked for thickness at 0.5 kPa using ISO 9073-2:2021, tensile strength using ISO 9073-3:2023, and pinhole density using a light-table inspection procedure with a threshold of 2 visible pinholes per m². A durable hydrophilic finish is applied at 0.30–0.50 % by weight; higher finish levels can transfer to calender rolls, lower levels produce intermittent liquid pooling on the cover surface. Cationic wetting agents are incompatible with the durable hydrophilic finish and can form insoluble complexes that cause surface energy variation. The material must comply with OEKO-TEX Standard 100 product class II for direct feminine-hygiene skin contact. The cover stock is converted into sanitary towels with polyethylene backsheet adhesive lamination, so storage is required below 50 % RH because electrostatic charge increases with moisture depletion and can disturb web guiding.

For adult incontinence briefs with a multilayer core architecture, the transfer layer is carded through-air bonded web with a basis weight of 30–60 g/m². The PP staple fiber is specified with high crimp and 2.0–3.0 dtex linear density, cut to 51 mm to reduce fiber shedding. Through-air bonding is run at 135–145 °C for 3.0–6.0 s residence time; the higher residence is necessary to stabilize the thicker web through the entire cross-section. Caliper retention under 0.5 kPa is measured by ISO 9073-2:2021 and should remain above 70 % of uncompressed thickness after 1 min recovery. Fluid acquisition is evaluated by repeated-dose strikethrough using 5 mL 0.9 % saline at 20 min intervals according to EDANA/INDA WSP 70.7; rewet after 3 doses is controlled below 0.15 g with a 2.5 kg load. The substrate must withstand converting tension at 400 m/min without necking more than 2.0 %; tension control is set to 10–15 N/m web width. OEKO-TEX Standard 100 product class II applies for direct skin contact in adult incontinence articles, and the fiber finish is selected to exclude bronopol and chlorinated phenols due to skin compatibility limits.

Carded through-air bonded panty liner cores for low-lint conversion

Panty liner absorbent cores are produced from PP staple fiber at 18–30 g/m² through air-through bonding. The structure combines 2.0–2.5 dtex crimped fiber cut to 40 mm to generate z-direction bulk without excessive stiffness. Through-air temperature is set at 132–142 °C; moisture content in the fiber must be below 0.10 % before bonding, otherwise caliper uniformity deteriorates because steam escaping from the web disrupts bond-point formation. The core is evaluated for caliper under 0.5 kPa with ISO 9073-2:2021, bending stiffness with ASTM D5732-19, and absorption capacity with ISO 9073-6:2021. Lint generation is measured by a rotary abrasion method; discharge to the surrounding machine frame should remain below 2.0 mg/m² to avoid contamination of adhesive coating lines. The finish package must be non-ionic and free of ethoxylated alkylphenols. The finished panty liner core is wrapped in nonwoven cover stock and sealed by ultrasonic bonding; the core must not exhibit melt-through at seam points. OEKO-TEX Standard 100 product class II compliance is required for direct skin contact.