GOHSENOL KL-05

GOHSENOL KL-05 is a partially hydrolysed polyvinyl alcohol resin in the GOHSENOL K-series, supplied as a granular solid and defined by the interaction between its degree of saponification and its low aqueous solution viscosity. The grade designation is not arbitrary: the numeric suffix 05 correlates with a nominal 4 wt% aqueous solution viscosity of approximately 5 mPa·s at 20°C, while the K-series designation locates the product among partially hydrolysed PVOH grades rather than fully hydrolysed N-series grades. The binding specification for any production lot is the certificate of analysis prepared under JIS K6726:1994, not the trade designation. In industrial use, the material functions as a high-purity water-soluble polymer. The residual acetyl groups along the polyvinyl alcohol backbone reduce the degree of crystallinity, lower the temperature required for hydration, and shift film-surface polarity relative to fully hydrolysed grades. These structural properties make the grade relevant to aqueous emulsion polymerisation, remoistenable adhesives, paper-coating vehicles, and water-based dispersion processes in which low solution viscosity at high solids is a controlling constraint.

What does the degree of saponification control in cold-water solubility?

The degree of saponification is the first specification boundary. Fully hydrolysed polyvinyl alcohol grades with a saponification degree of 98 mol% or more develop interchain hydrogen bonding dense enough to require dissolution temperatures above 80°C. KL-05 is widely specified in the partially hydrolysed band, commonly reported as 78–82 mol%. The residual acetate units break the stereoregular hydrogen-bonded network, allowing granules to hydrate at 20–25°C without prolonged high-temperature cooking. Viscosity is determined on a 4 wt% aqueous solution at 20°C; the commercial datasheet band is typically 4.5–5.5 mPa·s, measured with a Brookfield LV viscometer. The certificate of analysis reports lot-specific values, and the 4 wt% solution viscosity is the parameter used for incoming inspection because it detects both molecular weight shifts and drying-induced insolubles. Solution pH is typically controlled within 5.0–7.0. The product specification also limits ash content at or below 0.1 mass% and volatile content at or below 5.0 mass%.

These limits are relevant to electronic-grade or optical-coating applications where residual sodium acetate and water content can alter haze, adhesive peel, or solution ageing. The test procedures are drawn from JIS K6726:1994, but the supplier’s certificate of analysis remains the formal control document under ISO 9001 purchasing systems. The grade is also evaluated for degree of hydrolysis retention under accelerated storage. When a specification sheet gives a single viscosity value rather than a range, the value should be interpreted as a midpoint, not a tolerance. Published data for this specific configuration is limited when a converter requires a single-value viscosity for an in-process control chart; the certificate of analysis governs lot acceptance.

In aqueous make-down, the low-viscosity specification of KL-05 allows cold-water predispersion, but complete dissolution still requires controlled heating and mechanical shear. A production-scale make-down vessel is typically a jacketed stainless steel tank fitted with a Cowles-type high-shear disperser and a temperature probe. The granules are added through a screened funnel into the vortex while agitation is maintained at 300–500 rpm. The slurry is heated to 85°C and held for 30–60 min. Undissolved gel particles are removed through a 100-mesh stainless steel filter before transfer to the storage tank. At relative humidity above 60%, the resin absorbs atmospheric moisture. Predrying at 60–80°C for 2 h is applied before gravimetric batching to limit moisture-induced weighing error; this is a critical boundary because a 1 mass% moisture shift changes the active polymer concentration by the same amount and can push a high-solids coating outside its specified viscosity window.

The product is incompatible with high-valence metal salts at low pH, which can precipitate the polymer. Solution storage in unlined carbon steel is avoided because dissolved iron discolors the solution and reduces compatibility with optical brighteners. If the solution is held for more than 48 h at 35°C, a biocide approved for polyvinyl alcohol systems is required to prevent microbial growth in non-sterile production environments. For cleanroom use, the solution is filtered through a 5 µm absolute-rated cartridge and checked for turbidity below 5 NTU before release. These controls are not optional when the formulated product is used in optoelectronics or pharmaceutical transfer films.

Protective Colloid Performance in Vinyl Acetate Emulsion Polymerisation

The choice of KL-05 in emulsion polymerisation is a balance between colloidal stability, final latex viscosity, and grafted polymer fraction. In a 1,000 L batch reactor with a 45° pitched-blade turbine operating at 120 rpm, a typical addition of 3.0 wt% KL-05 based on total monomer mass provides steric stabilisation of vinyl acetate droplets and particles without raising the final latex viscosity beyond the transfer range of diaphragm pumps. The residual acetate groups participate in radical transfer to the polymer backbone during vinyl acetate polymerisation. This lowers the frequency of irreversible grafting onto the colloid compared with fully hydrolysed grades; the practical consequence is lower Brookfield viscosity drift after 14-day storage at 40°C. The low aqueous viscosity of KL-05 also allows higher colloid loadings before the pre-emulsion becomes too thick for the reactor’s circulating loop.

The grade is not appropriate when maximum water resistance of the dried film is required. The hydroxyl-rich colloid surface absorbs water unless a crosslinker or a higher-hydrolysis co-colloid is specified. In polymerisation reactors with severe mechanical shear, such as rotor-stator pre-emulsifiers operated above 3,000 rpm, KL-05 maintains droplet stability but may require an additional anionic surfactant to control particle size below 300 nm. Published data for this specific configuration is limited, and reactor-scale validation is required because the particle size distribution is affected by initiator feed rate, agitation power input, and the presence of acetate buffer.

When cold-water rewetting is required in remoistenable adhesive coating lines

Remoistenable adhesive coatings require a polymer that dries to a non-blocking film yet rehydrates rapidly when wetted. An 8 wt% aqueous solution of KL-05 can be applied through a 250-line gravure cylinder at 150 m/min; the low solution viscosity permits clean cell evacuation, and the partially hydrolysed chain architecture allows rewetting within 3–5 s when a water droplet is applied at 25°C. The dry coat weight is typically 3–5 g/m². Under these conditions, the product forms a continuous film but does not reach the tensile strength of a higher-viscosity partially hydrolysed grade.

Coating lines that use air-knife or roll-coating equipment benefit from the viscosity ceiling of KL-05: at 8 wt%, the solution viscosity remains low enough to avoid film splitting at speeds above 120 m/min. The low ash content keeps dried-film haze low under a 20° gloss measurement geometry, a feature that is relevant when printed graphics are applied over the adhesive layer. The operational boundary is set by film strength and moisture resistance, not by dissolution. If the coated paper is exposed to relative humidity above 70% before converting, blocking can occur; an anti-blocking agent or a harder co-resin is required. For remoistenable label stock, the rewetting time is measured with a 10 µL water droplet on a standard A4 paper substrate under 23°C and 50% relative humidity.

On a production paper-coating line, KL-05 is typically evaluated at 2–6 wt% in a coating colour containing precipitated calcium carbonate and kaolin. The low aqueous viscosity reduces thickening in high-solids blade-coating formulations. A blade coater running at 1,000 m/min requires a low-shear viscosity below 300 mPa·s at 25°C to maintain coater runnability. KL-05 at 4 wt% solution viscosity of 4.5–5.5 mPa·s allows the formulator to add more pigment before the coating colour reaches the blade-coater high-shear viscosity limit. The binding strength of the dried coating is lower than that of a fully hydrolysed or higher-viscosity grade; therefore latex binders are used as the primary binder and KL-05 functions as a water retention and rheology additive. In continuous warp sizing, a cook kettle at 95°C is used to prepare a 6 wt% solution; the low-molecular-weight grade penetrates the yarn bundle and improves abrasion resistance without excessive warp stiffness. The size film loses tensile strength under high-humidity weaving sheds; humidification above 70% relative humidity can cause loom droppings. Published data for this specific configuration is limited.

Fully hydrolysed grades impose a hotter dissolution boundary.

Comparisons with other GOHSENOL grades are made on the basis of 4 wt% viscosity and degree of saponification rather than film colour or granule size. Fully hydrolysed N-series grades with solution viscosities in the 25–30 mPa·s range and saponification above 98 mol% provide higher tensile strength and water resistance. They require hot-water dissolution above 80°C and can raise mix viscosity beyond the limit of air-knife coaters. The cost of using KL-05 is therefore a reduction in wet strength and water resistance, not a reduction in solubility. Higher-viscosity partially hydrolysed K-series grades retain cold-water solubility but generate more viscous solutions at equal solids. Their films are tougher, but their transfer and levelling on high-speed roll coaters are more difficult.

KL-05 occupies the low-viscosity end of the partially hydrolysed range. The selection rule is straightforward: where aqueous solubility after drying is the primary specification, KL-05 is specified; where a permanent moisture barrier or high film tensile strength is required, the formulator selects a fully hydrolysed grade or adds a compatible crosslinker. The product should not be combined with amine-based additives that raise solution pH above 9.0; under high-pH ageing, ester residual groups can hydrolyse, shifting the effective degree of saponification and changing rewetting time. For food-contact applications, compliance with regional positive lists, including 21 CFR sections relevant to the specific food type and use condition, must be confirmed on the final formulated article; the neat resin datasheet is not a sufficient regulatory clearance.