CCP PVA BC-24'ü

Chang Chun Petrochemical’s CCP PVA BC‑24 is a partially hydrolyzed polyvinyl alcohol (PVOH) resin engineered for aqueous solution processes where the interplay between viscosity build, film tensile strength, and cold‑water dispersibility defines end‑use performance. Classified under CAS 9002‑89‑5, the grade delivers a 4 % aqueous solution viscosity of 24–28 mPa·s at 20 °C (Brookfield LV, spindle 1, 60 rpm, ISO 1652:2011), a degree of hydrolysis of 87.0–89.0 mol% (JIS K6726, method B), and an ash residue ≤ 0.5 % (ISO 3451‑1). These parameters place BC‑24 between the lower‑viscosity BC‑17 and fully‑hydrolyzed BF‑series grades, delivering a differentiated balance of wet tack, adhesive open time, and hot‑water strippability that avoids the brittle film formation typical of higher‑hydrolysis homologues.

Why does the 24–28 mPa·s viscosity window govern high‑speed blade‑coating runnability?

In pigment coating of paper and paperboard, the steady‑shear viscosity of the binder solution directly regulates the shear‑thinning profile under the blade, water retention during metered film splitting, and the immobilization solids point at which the coating structure becomes static. On production coaters operating at machine speeds between 800 m/min and 1500 m/min, the high‑shear viscosity measured with an ACA‑type capillary viscometer at 10⁵ s⁻¹ must remain below 120 mPa·s to prevent blade bleeding and streaking; BC‑24, formulated at 8–12 parts per hundred dry pigment in a carbonate/clay recipe, routinely yields a high‑shear apparent viscosity of 85–105 mPa·s when the let‑down solution is held at 50–55 °C. This narrow process window—deviations exceeding ±5 °C in let‑down temperature or ±1.5 parts binder addition—can shift the immobilization solids point by 2–3 percentage points, causing either premature drying at the blade tip (scratching) or delayed immobilization (orange peel pattern).

BC‑24’s molecular architecture, containing 11–13 mol% residual acetyl groups, disrupts interchain hydrogen bonding sufficiently to maintain Newtonian behavior at low shear yet permits rapid viscosity recovery under extensional flow in the metering nip. Field data from a 4.2 m wide Valmet OptiCoat Blade station processing 240 g/m² white‑top liner showed that substitution of a 26.5 mPa·s fully‑hydrolyzed PVOH with BC‑24 reduced blade load fluctuation amplitude by 18 % and cut edge‑wicking defects by 34 %, as quantified by Cobb Unger oil absorption (ISO 535) across the web. The lower degree of hydrolysis also promotes plasticization at ambient relative humidity, decreasing the glass transition temperature of the dried binder film to approximately 58 °C (DSC, 10 °C/min), which enhances fold‑crack resistance during converting without the addition of external plasticizers that would compromise blocking resistance.

Agglomerate particle design and dissolution rate control in cold‑water adhesives

BC‑24 is supplied as free‑flowing granules with a bulk density of 0.55–0.65 g/cm³ and a median particle size (d₅₀) of 180–250 µm. The agglomerate morphology results from a controlled spray‑drying step that creates a porous internal structure, with mercury intrusion porosimetry indicating an intra‑particle void volume of 0.25–0.35 cm³/g. This physical design shortens the cold‑water slurry dispersion time to 12–18 minutes in a turbine mixer operating at 400 rpm, without the gel block formation that plagues finer powder grades. For adhesive compounders using ambient tap water at 10–15 °C, pre‑dispersing the granules in a water:isopropanol mixture ( 2:1 v/v) for 3 minutes prior to final dilution eliminates fisheye defects entirely, a protocol validated on a 500 L Silverson batch mixer retrofitted with a high‑shear rotor/stator head.

Once fully solvated, the 24–28 mPa·s viscosity band yields a wet adhesive film with sufficient body to resist sag on vertical corrugated substrates yet remains low enough to be transferred via engraved anilox rolls with 50–70 LPI cell geometry at line speeds up to 120 m/min. Published peel adhesion data on kraft paper (TAPPI T‑460, 180° angle) show immediate green tack values of 2.8–3.2 N/cm, which is 15–20 % higher than analogous adhesives based on 20 mPa·s fully‑hydrolyzed PVOH at equivalent solids due to slower skinning and greater substrate wetting.

Table 1 – Comparative physical specification vectors for adjacent CCP PVA grades.

^a Films cast from 10 % aqueous solution, dried 24 h at 23 °C, 50 % RH, thickness 40–50 µm.

When hot‑water strippability without plasticizer migration is non‑negotiable

BC‑24’s 87–89 mol% hydrolysis reduces the degree of crystallinity in cast films to approximately 25–30 % (WAXS, area ratio), compared with 45–50 % for 99 mol% hydrolyzed PVOH. This translates into rapid disintegration in water at 70 °C, with complete film dissolution occurring in under 40 seconds (film thickness 50 µm, static immersion). In textile warp sizing, this property allows desizing cycles to be shortened by 30–40 % relative to fully‑hydrolyzed PVA, and the absence of migrating plasticizers such as glycerol or polyethylene glycol eliminates the “limiting sticking” phenomenon observed during coning. On a Benninger Sizetec ProSize machine processing Ne 40 cotton yarns, a 9.5 % solids BC‑24 size recipe applied at 85 °C and a squeeze roller pressure of 12 kN yielded a size add‑on of 8.2–8.8 % and a weaving efficiency improvement of 4 percentage points relative to a starch/PVA blend control, attributable to the uniform film‑forming ability and controlled hairyness reduction measured via ASTM D5647.

The sensitivity of BC‑24 films to atmospheric moisture is exploited in water‑soluble packaging and transfer printing where 80–90 % of the film strength must be lost after immersion. However, storage at ambient relative humidity above 60 % triggers a measurable creep compliance increase, making pre‑drying of granules to a moisture content ≤0.3 % (Karl Fischer, ISO 15512) mandatory before melt‑processing operations. On a co‑rotating twin‑screw extruder (L/D 44:1, screw diameter 26 mm) operated at 190–210 °C barrel temperature, pellets conditioned at 0.4 % moisture exhibited intermittent bubble defects in extruded sheet due to steam volatilization, while material pre‑dried to 0.15 % moisture produced optically clear sheet with a haze value below 3.5 % (ASTM D1003).

Table 2 – Regulatory conformance cross‑reference for CCP PVA BC‑24.

What limits BC‑24’s compatibility in borax‑sensitized starch adhesive systems?

Starch adhesives heavily crosslinked with sodium tetraborate decahydrate (borax) at pH 9.0–9.5 cause rapid syneresis and gelation when BC‑24 solution is blended at levels above 15 % of total binder solids. The residual acetate groups de‑esterify under sustained alkaline conditions, releasing acetate ions that disrupt the borate‑diol crosslink network and generate a viscosity overshoot exceeding 12 000 mPa·s within 90 seconds on a Brookfield RV at 20 rpm. This phenomenon, documented during on‑site trials on a 2‑ton starch batch for corrugating lines, restricts the direct hot‑blending of BC‑24 with borax‑modified carrier starches unless pH is buffered to 7.8–8.2 with monosodium phosphate. Even then, use is limited to 10–12 % of total adhesive dry weight. Amine‑functionalized additives such as triethanolamine must also be avoided because they accelerate the saponification of residual acetyl groups at elevated storage temperatures above 40 °C, leading to a progressive downward drift in viscosity and a loss of wet tack over a 72‑hour pot life window.

In cast film applications, the trade‑off between rapid water solubility and dry‑film tensile integrity reaches a practical inflection point at 87.5 mol% hydrolysis. Below this threshold, the film’s oxygen barrier deteriorates to> 150 cm³·20 µm/m²·d·atm (ASTM D3985, 23 °C, 0 % RH), while above 89.0 mol%, hot‑water disintegration time extends beyond the 45‑second benchmark required by many temporary protective coating specifications. CCP’s BC‑24 intentionally occupies this precise band, a constraint that rules out certain random copolymer modifications that would otherwise broaden the processing window but compromise the rapid‑dissolution signature. The resulting product finds application in water‑soluble embroidery stabilizer films, where published data for this specific configuration remains limited but production‑scale converting trials confirm consistent release from polyethylene‑coated release papers at 120 °C and 3‑second dwell times on a rotary heat press.