Alcohol polivinílico (PVA) para tubos de papel y adhesivos de núcleo

Spiral Tube Winding at Line Speeds Exceeding 80 m/min

Partially hydrolysed PVA with a hydrolysis degree of 87–89 mol% and a 4 % aqueous solution viscosity of 20–28 mPa·s at 20 °C constitutes the primary binder in high-speed spiral tube winding for adhesive tape cores and textile yarn carriers. The adhesive is prepared as a 12–14 % solids dispersion at 50–55 °C in a jacketed mixing tank equipped with a slow-speed anchor agitator operating at 20–30 rpm to avoid air entrapment. Kaolin filler (5–8 % on wet weight) is introduced via an eductor to increase dry grab and reduce cold-flow tendency. The fully formulated mix is recirculated to a glue pan maintained at 22–28 °C by a heat-exchange jacket; viscosity measured in-line with a Brookfield viscometer fitted with an RV spindle No. 3 at 20 rpm is held at 1200–1800 mPa·s. Dip-pickup on single-face or double-face liner of 160–220 g/m² must deliver a wet film weight of 45–55 g/m² to achieve a dry add-on of 5–7 g/m² per ply. Tension control across the EPC web guide and the polyurethane drive belt should maintain a winding angle of 52–55° and a belt pressure of 0.2–0.4 MPa; deviation beyond ±2° shifts the ply alignment and causes visible spiral seams that reduce beam strength. Infrared post-heating modules set to a surface temperature of 90–110 °C for a dwell time of 8–12 s evaporate water to a residual moisture of 6–8 %. A frequent production-floor fault is skin-over blistering, occurring when the surface film crosslinks prematurely under infrared flux faster than the core can vent vapour; the remedy is to reduce the first-zone IR emitter intensity by 15–20 % or to increase the fan-forced convection component. End-of-line tensile splitting resistance is tested per TAPPI T 821 with a spindle pull-out fixture; a minimum of 650 N/100 mm of tube wall circumference is typical for apparel-grade yarn carriers. In applications where the tube must survive automated doffing, a small addition of glyoxal (0.3–0.6 % of PVA dry weight) is pre-mixed at pH 5.5–6.0 buffered by sodium acetate; the pot life of this mix is 6 h at 25 °C, beyond which viscosity drift exceeds 15 %. This additive acts as a latent crosslinker during the drying stage and raises the wet green strength enough to prevent ply slipping at the cut-off knife. Material handling incompatibilities must be flagged: contact with bronze de-watering rolls can leach copper ions that discolour the PVA film, and storage of liquid adhesive in unlined carbon-steel tanks introduces ferric ions that catalyse chain scission under heat.

Typical Partially Hydrolysed PVA Grades for Spiral Tube Winding — Viscosity Response and Dry Bond Strength

PVA Grade (hydrolysis mol%)	Brookfield Viscosity 12 % sol. @ 25 °C (mPa·s)	Dry Ply Adhesion TAPPI T 821 (N/100 mm) at 6 g/m² add-on	Wet Strength Retention after 10 min soak (%)
04-88 (87–89 %)	800–1100	720	28
17-88 (87–89 %)	1300–1800	910	34
24-88 (87–89 %)	2200–2800	1050	41
26-88 (87–89 %)	3000–3800	1100	44

Heavy-wall parallel-wound cores destined for PET film or newsprint mill roll builds demand a cold-water-soluble binder that penetrates fully into 250–400 g/m² kraft liner without surface dusting. A mixed-cook of an oxidised potato starch (60–70 % of total dry solids) and partially hydrolysed PVA 17-88 (30–40 % of dry solids) is prepared by first gelatinising the starch at 82–86 °C in a scraped-surface continuous cooker, cooling to 50 °C, and then dosing the pre-dissolved PVA solution under slow sweep agitation. The combined adhesive, at 18–22 % total solids, exhibits a viscoelastic character with a zero-shear viscosity of 3000–5000 mPa·s and a short, non-stringy flow profile that prevents throw-off at applicator roll speeds of 60–120 m/min. Coating is performed via a two-roll differential speed metering station where the rubber-covered pick-up roll runs 15–20 % slower than the chrome-plated doctor roll, yielding a controlled coat weight of 8–10 g/m² dry across a web width of up to 2500 mm. During winding, the independently driven pressure roll exerts 6–8 bar of line force, compacting the plies before the adhesive enters its drying phase in a multizone tunnel with an air temperature ramp from 60 °C to 130 °C. Radial crush strength measured by the edge crush test according to ISO 3037:2022 should reach 4.5–6.0 kN/m for a 10 mm wall thickness to support a substrate roll weight exceeding 1.5 tonnes. A documented processing limit is the susceptibility of cooked starch-PVA blends to biological spoilage; the pot temperature must remain above 45 °C and the holding tank should be steam-cleaned every 72 h. The addition of 1,2-benzisothiazolin-3-one at 50–100 ppm extends open time to 96 h but may interfere with fluorescence-based inline glue detection, a factor to coordinate with quality assurance.

When Moisture Resistance Must Exceed 24-Hour Immersion

Fully hydrolysed PVA with a hydrolysis degree of ≥98.5 mol% and a molecular weight corresponding to a 28–35 mPa·s viscosity (4 % aq., 20 °C) is the preferred base for water-resistant tube adhesives used in frozen food wrap cores and outdoor formwork tubes. The aqueous solution at 10–12 % solids is joined by a latent acid catalyst, typically magnesium chloride hexahydrate at 3–5 % of PVA dry matter, and a blocked crosslinker, such as dimethyloldihydroxyethyleneurea (DMDHEU) or butanetetracarboxylic acid, added at 8–12 % on PVA weight. The wet gel coat, transferred to the paper at 35–45 g/m², requires forced thermal activation in a radio-frequency-assisted convection heater delivering a product temperature of 130–140 °C for 20–30 s to achieve covalent esterification or etherification. Laboratory condom-immersion tests simulating 23 °C water contact for 24 h must show a wet-to-dry ply adhesion retention above 60 % when tested per TAPPI T 812. In freezer-grade cores stored at -25 °C, the adhesive layer must remain flexible and resist crack formation caused by moisture crystallisation; this is verified by subjecting tubes to 10 cycles between -25 °C and +40 °C at 95 % relative humidity without delamination. The pot life of the catalysed mix is no longer than 4 h at 25 °C, mandating two-component metering at the point of application or periodic purging of the glue delivery loop. Equipment cleaning protocols use a 5 % acidic peroxide solution to remove thermoset residues from chrome surfaces. An operational incompatibility exists with amine-functionalised sizing agents present in some recycled liners; the amine can prematurely deblock the crosslinker and form a brittle interphase that fails under impact.Dense convolute tubes for the pyrotechnic industry are manufactured by rolling multiple plies of unbleached kraft under a load of 0.5–1.0 MPa around a polished mandrel after saturating the paper with a low-viscosity, fast-penetrating PVA solution. The binder of choice is grade 04-88 at 8–10 % solids, into which 3–5 % glyoxal (dry basis) is stirred at 15–18 °C to impart sufficient wet-raked strength that the tube maintains its circularity during the wet-burst phase of pyrotechnic combustion. Internal bond testing according to TAPPI T 833 pm-94 should yield a Z-direction tensile strength not less than 520 kPa. Post-winding conditioning in a humidity cabinet set to 60 °C and 50 % RH for 90 min completes the hemiaminal crosslinking reaction while relaxing longitudinal stress. A critical processing fault manifests as star-shaped end fractures: this occurs when glyoxal dosage exceeds 6 % or when the tube stock is stored below 35 % RH, causing overdrying and embrittlement of the PVA film. Manufacturing control relies on a mandrel-release force meter; values deviating more than 15 N from the setpoint indicate incomplete cure or excessive moisture absorption from ambient air above 65 % RH.

Compostable Core Stock and EN 13432 Validation

PVA homopolymer of grade 13-88 combined with a thermoplastic hydroxypropyl starch at a 50:50 dry-weight ratio produces an adhesive film that disintegrates completely in industrial composting conditions. The formulation is pigment-free and contains no boron compounds, as borate ions chelate the PVA hydroxyls and reduce microbial accessibility. Lamination of unbleached, FSC-certified kraft paper uses a dry coat weight of 4–6 g/m² and follows the spiral-tube process described earlier, after which the core is cut to length without synthetic lacquer edge-sealing. Disintegration is evaluated under ISO 16929:2021 at 58 ± 2 °C for 12 weeks; fragments retained on a 2 mm sieve must not exceed 10 % of the original dry mass. Acute ecotoxicity of the compost must conform to OECD 208 plant germination limits. In accelerated ageing tests simulating six-month warehouse storage in south-east Asia (38 °C, 85 % RH), the compressive strength drops by 12–18 %, which must be factored into the safety margin when specifying wall thickness. Because the fully bio-based formula offers no built-in biocidal protection, the converted cores must be wrapped in a vapour-barrier foil within 24 h of production.

Adhesive Compliance with FDA 21 CFR 176.170 for Indirect Food Contact

Paper cores wound with PVA destined to carry aluminum foil or polyethylene-coated food wrap rolls must comply with the component limitations of 21 CFR § 176.170, Table 2. The permitted PVA resin is manufactured to meet the residual vinyl acetate monomer ceiling of 5 mg/kg and methanol below 1 %, confirmed by headspace GC-MS on every production batch. The compounded adhesive incorporates food-grade plasticisers — glycerol or sorbitol — at 3–5 % of wet formulation to prevent film brittleness and eliminates all amine-catalysed crosslinkers. Extraction tests with n-heptane (38 °C, 30 min) and 8 % ethanol (49 °C, 24 h) according to the corresponding food-type classifications must yield total non-volatile extractives below 0.5 mg/in² of contact surface. Air-knife stripping of the freshly glued ply removes low-molecular-weight fractions that might otherwise migrate into the food-contact material through the intervening layers. Production equipment is restricted to stainless steel 304L or higher alloy; threaded brass fittings are excluded to avoid zinc and copper contamination. Periodic microbial audits using 3M Petrifilm plates verify the absence of coliforms; without preservative agents, the adhesive holding tank must be completely drained and sanitised with 80 °C de-ionised water at the end of each workshift.