GOHSENOL NK-05R

In high-speed shuttleless air-jet and rapier weaving, the warp size film must survive cyclic abrasion from drop wires, heald eyes, and reed dents without generating the fibre hairiness that forces machine stops. GOHSENOL NK-05R, with a 4% aqueous solution viscosity of 5.0–6.0 mPa·s at 20 °C and a hydrolysis degree of 98.0–99.0 mol%, is selected where low size add-on and deep bundle penetration are required simultaneously. In a polyester/cotton warp size formulation, the size liquor is compounded at 8–12% total solids, with NK-05R at 20–40% of total size solids, native or modified starch at 60–75%, wax-type lubricant at 5–10%, and antistatic agent at 0.5–1.0% on dry solids. The liquor is cooked in a jet cooker at 110–130 °C for 20–30 min, then held at 85 °C and applied in a size box at 75–85 °C with squeeze-roll pressure adjusted to target 80–110% wet pickup. Because the fully hydrolyzed film is not removed efficiently by amylase-only desizing, downstream desizing requires 0.5–1.0% sodium hydroxide and 0.3–0.5% wetting agent at 70–80 °C. Weaving performance is tracked by warp break frequency per 100,000 picks, yarn hairiness by a Zweigle G567 tester, sized-yarn abrasion resistance by ASTM D3885, and size film tensile behaviour adapted from ASTM D882. The formulation must avoid APEO-based surfactants under ZDHC MRSL v3.1, and the PVOH component itself is REACH registered. Mill-scale failure modes include size-box solids drift from evaporation at 80 °C and foam carryover from high-shear circulation, both of which are managed by online refractive-index solids control and a deaerating size-box feed system.

Paper Surface Sizing and Pigmented Coating Binder Demand at the Metering Size Press

Surface sizing of copy paper, envelope stock, and folding boxboard uses NK-05R as a low-viscosity co-binder with oxidised starch at a metering size press. The starch component is cooked at 90–95 °C for 30 min; NK-05R is dissolved separately at 8–10% solids and added to reach 1–3 parts PVOH per 100 parts starch solids. The sizing solution is applied at 55–65 °C and 6–12% solids through a film press such as a Voith SpeedSizer or Valmet OptiSizer, with dry pickup of 1.0–2.5 g/m² per side. To control rewetting of the fully hydrolyzed PVOH film during offset printing, an insolubilizer is required: 0.1–0.5% ammonium zirconium carbonate or 1–3% glyoxal based on PVOH solids. In pigmented coating colour, NK-05R is predissolved at 10% solids and metered at 0.3–1.5 parts per 100 parts pigment to increase water retention and low-shear viscosity without raising high-shear coating viscosity excessively. Coating-colour viscosity is measured by low-shear Brookfield viscometer at 25 °C and 100 rpm per ISO 2555. Coated surface strength is tested by IGT pick velocity according to ISO 3783, water absorption by Cobb 60 according to ISO 535, and air permeability by Gurley according to TAPPI T460. For food-contact paper and board, the use of PVOH as a size-press additive is covered under FDA 21 CFR 176.170 and EU Regulation 1935/2004, with overall migration controls per EU Regulation 10/2011 where applicable. The low ash content of NK-05R, below 0.5%, reduces deposit formation on metering rods and backing roll surfaces during continuous campaigns, while the low solution viscosity permits higher starch solids without press-roll film splitting problems.

What Happens When a Low-Viscosity Fully Hydrolyzed PVOH Serves as Protective Colloid in VAE Emulsion Polymerization?

The protective colloid function of NK-05R in vinyl acetate/ethylene and vinyl acetate homopolymer emulsion polymerisation is governed by graft reaction kinetics at the particle surface and by low-shear rheology in the reactor. Fully hydrolyzed PVOH with 98.0–99.0 mol% hydrolysis provides a high density of hydroxyl groups available for chain transfer with polyvinyl acetate propagating radicals, producing a grafted PVOH layer around polymer particles. The low molecular weight of NK-05R, indicated by the 5.0–6.0 mPa·s viscosity of a 4% aqueous solution at 20 °C per JIS K6726, permits higher solids operation before viscosity limits are reached. A 10% PVOH stock solution is prepared at 90–95 °C for 60 min and filtered through a 250 µm screen before transfer. In a batch reactor charged to 1000 parts, vinyl acetate monomer is loaded at 350–450 parts, 10% PVOH solution at 80–120 parts, potassium persulfate initiator at 0.2–0.5 parts, sodium bicarbonate buffer at 0.3–0.6 parts, and the balance is deionized water. Polymerisation is controlled at 70–80 °C with an anchor impeller running at 60–100 rpm. The final emulsion commonly reaches 50–55% solids per ISO 3251 and Brookfield viscosity of 2000–8000 mPa·s at 25 °C per ISO 2555. PVOH-stabilised vinyl acetate emulsions typically show particle sizes in the 0.5–2.0 µm range. The dried film has moderate water resistance because residual PVOH is hydrophilic; where water resistance is required, post-added crosslinkers such as glyoxal or AZC are introduced. Adhesive applications may fall under FDA 21 CFR 175.105, subject to migration limits in the finished package. Reactor fouling and viscosity drift are the main operational limits: insufficient PVOH grafting produces coarse particles, while excessive PVOH raises finished emulsion viscosity beyond the target range.

Ceramic Tape-Casting Binder and Burnout Profile Management

Doctor-blade tape casting of alumina, barium titanate, and LTCC substrates uses fully hydrolyzed low-viscosity PVOH as a temporary binder that provides green strength before burn-out. The low ash content below 0.5% is critical because residual sodium or heavy metals from higher-ash grades can alter dielectric loss, contaminate grain boundaries, or leave carbon residue after sintering. A water-based alumina slip is prepared first by milling ceramic powder, dispersant, and water, then adding a separately dissolved 10% NK-05R solution at 90–95 °C for 45–60 min and cooling it to 25–30 °C. The milled slip is processed in a polyurethane-lined mill with 10 mm zirconia media at 60 rpm for 24 h, then the binder and plasticizer are mixed in, followed by deairing under -0.09 MPa vacuum for 30 min. The slip is cast through a doctor blade with a gap of 200–600 µm onto a silicone-coated polyester carrier moving at 0.5–1.5 m/min. Drying is conducted at 25–35 °C and 50–60% relative humidity to prevent skinning, and the green tape is produced at 100–300 µm dry thickness. Green tape handling is specified at 45–55% RH because moisture absorption reduces tensile strength and increases variability. For burn-out, the tape is heated from 200 °C to 450 °C at a ramp rate no greater than 2 °C/min, then held at 450–500 °C for 1 h to oxidise the PVOH. Thermogravimetric analysis according to ISO 11358-1 confirms that no organic residue remains above 500 °C. Published data for green tensile strength of this specific NK-05R tape-casting formulation is limited; tensile strength should be verified using ASTM D638-14 adapted to thin films.

In spiral-wound paper tube and convolute core manufacturing, the adhesive must build tack quickly between moving plies without soaking the board and causing curl or ply delamination. NK-05R is pre-dissolved at 10% solids and formulated with kaolin clay at 10–20 parts, glycerin at 1–3 parts, defoamer at 0.1–0.3 parts, and preservative at 0.05–0.1 parts per 100 parts of 10% PVOH solution. The adhesive is applied at 40–50 °C by roll or doctor blade at a wet film weight of 10–30 g/m². Line speed on a spiral tube winder is typically 20–60 m/min, so the adhesive must develop green tack within the short open time between ply application and winding pressure. A critical processing boundary is that borate or boric acid addition must be avoided or strictly limited because the high diol content of fully hydrolyzed PVOH reacts with borate ions to form a reversible but strong gel network, which can lock up transfer pumps and coating rolls. Viscosity is controlled at 500–2000 mPa·s at 25 °C per ISO 2555 to maintain pumpability. Finished core compression strength is monitored on a column crush tester, although published data for this specific configuration is limited. The low-foam formulation and pH 5.0–7.0 solution compatibility with paper mill water are primary reasons for selecting NK-05R over high-viscosity PVOH grades that build excessive adhesive viscosity at the same dry solids.

When NK-05R Is Used as a Remoistenable Adhesive Base for Envelope and Label Gumming

A remoistenable adhesive formulated from NK-05R is applied to envelope flaps, label stock, and gummed tape by reverse gravure or kiss-roll coating. The dried film must remain non-blocking under normal storage humidity but rewet rapidly at 20–25 °C and develop tack within 3–5 s. A typical formulation contains 100 parts of 10% PVOH solution, 20–40 parts dextrin, 2–5 parts glycerin, 0.1–0.3 parts wetting agent, and 0.1 parts preservative. The adhesive is held at 40–50 °C during application and applied at a dry coat weight of 5–15 g/m². Viscosity is maintained at 300–1200 mPa·s at 25 °C per ISO 2555. Because NK-05R is fully hydrolyzed, the remoistened film has higher cohesive strength and lower cold-water solubility than partially hydrolyzed grades, producing harder tack after drying but requiring a wetting agent to accelerate re-wetting. The dry film is less likely to block at 60% relative humidity than a partially hydrolyzed PVOH of similar molecular weight. For food-contact packaging, the adhesive may be used under FDA 21 CFR 175.105, provided migration limits are satisfied in the intended application. Borate crosslinkers are generally excluded to avoid gelation. Mill optimisation typically focuses on balancing dextrin level against PVOH content: too much dextrin lowers film strength, while too little raises cold-viscosity and slows remoistening.