KURARAY POVAL 28-99 LA

In ceramic tape casting for low-temperature co-fired ceramic substrates, KURARAY POVAL 28-99 LA is applied as a temporary binder in an aqueous slip system where residual alkali metal carryover must be limited to avoid dielectric loss and silver conductor migration during co-firing. The grade is dissolved in deionised water at 80–90 °C under low-shear agitation to prepare a stock solution of 8–12 wt% solids; after cooling to 25–30 °C, the solution is held under vacuum for 2–4 h to remove entrained air. The specification relevant to process control is a 4 % aqueous solution viscosity of 27–29 mPa·s at 20 °C by JIS K6726, with a degree of hydrolysis of 99.0–99.8 mol% that leaves minimal residual acetate groups and thereby reduces plasticisation of the dried binder film by atmospheric moisture. In an alumina or glass-ceramic slip, binder solids are metered at 4–8 wt% of the inorganic powder weight, with plasticiser at 2–4 wt% of powder weight and a polyelectrolyte dispersant at 0.5–1.0 wt%. The slip is milled until no visible agglomerates remain, deaired, and cast through a doctor blade gap of 100–300 µm onto a polyethylene terephthalate carrier at a line speed of 0.5–1.5 m/min. Drying is controlled at 60–80 °C, producing a green tape thickness of 50–200 µm; production experience shows that dryer air above 85 °C creates a surface skin that traps residual water and causes curling or delamination during blanking, while carrier tension above 50 N/m can initiate transverse cracking at the blade exit. Before lamination, green sheets are stored below 40 % RH to prevent dimensional change from moisture pickup. The green sheets are blanked, screen-printed with silver or copper conductor paste, laminated, and sintered according to the inorganic system; terminal components include low-temperature co-fired ceramic modules, sensor substrates, and multilayer ceramic interconnect sheets. Fired substrate quality is checked by ASTM C373-18 for fired density and by internal sodium oxide extraction procedures because the LA designation targets contaminant-sensitive ceramic processing; exact alkali limits must be taken from the lot certificate of analysis.

Spray-Dried Ceramic Press Granules and Binder Migration Control

In dry pressing of technical ceramics, 28-99 LA is introduced as a spray-drying binder to convert a milled aqueous slurry into free-flowing press granules. The binder solution is prepared at 5–10 wt% solids and metered into the ceramic slip so that the final binder content is 0.8–2.0 wt% of dry ceramic powder. The slurry is atomised in a co-current spray dryer equipped with a rotary atomizer or two-fluid nozzle; inlet temperature is held at 180–220 °C, and outlet temperature is kept below 95 °C to prevent glass-transition-driven sticking and thermal yellowing of the fully hydrolysed polymer. Discharged granulate is cooled to 40–60 °C with a target moisture content below 0.5 wt%. The critical defect on production lines is binder migration during evaporation: as water leaves the droplet, soluble PVOH migrates to the surface and forms a dense shell that resists crushing during compaction and lowers green density. Feed solids above 70 wt% thicken the shell, while very fine atomisation below 20 µm median droplet diameter increases dust and accelerates surface migration. A rotary atomizer tip speed of 120–180 m/s is commonly used to form granules with a median diameter of 60–150 µm and an angle of repose below 30°. The granulate is pressed in hydraulic or mechanical presses at 80–200 MPa; binder levels below 0.8 wt% cause edge chipping during demoulding, whereas levels above 2.0 wt% increase debinding load without proportional green strength gain. Debinding is conducted at 0.5–1.0 °C/min to 450 °C with an oxidative hold, followed by high-temperature sintering. Terminal products include alumina, zirconia, and silicon nitride wear tiles, pump seals, valve components, and net-shape technical ceramic parts. Alkali residues are checked against the controlled-alkali lot certificate and by residual ash after 600 °C oxidation; if electroceramic applications impose tighter alkali ceilings, lot-specific sodium and potassium measurement is required because the LA grade does not eliminate all alkali species.

Surface sizing of fine paper with fully hydrolysed polyvinyl alcohol changes the film-forming mechanism compared with oxidised starch because the PVOH chain forms a continuous film at lower add-on and alters the wetting behaviour of the sheet without the same moisture blushing sensitivity. In a metered-film or rod metering size press, 28-99 LA is prepared as a 2–6 wt% aqueous solution at 50–65 °C, and the bath pH is maintained between 6 and 8. The size add-on is controlled at 0.5–2.0 g/m² per side according to the base sheet and end-use. When the grade is used as a partial replacement for oxidised starch, the PVOH fraction may be 20–50 % of total size solids; above this fraction, the sized sheet becomes less rewettable and can disturb ink absorption or repulping in mill broke. On paper machines exceeding 1200 m/min, the solution is filtered through 50–100 µm screens because undissolved particles cause streak defects at the metering rod. The process target is surface strength and reduced linting on offset and digital printing grades; terminal paper products include inkjet base paper, thermal paper base stock, and release liners. The controlled alkali profile of the LA grade is relevant for thermal paper base stock because extractable sodium ions can interfere with the leuco dye developer layer and affect image stability. Sized-sheet performance is evaluated by ISO 8791-4 for surface roughness and by tensile strength retention tests after sizing; mill trials should account for increased white-water foaming in closed water circuits when fully hydrolysed PVOH is present with retention aid residues.

What Controls Open Time in Remoistenable Water-Activated Adhesive Coatings?

Remoistenable adhesive formulations based on 28-99 LA are used for labels, envelopes, and wallpaper seams where a dry film must remain non-blocking during storage and develop wet tack after water activation. The polymer is dissolved at 20–30 wt% solids in a heated jacketed mixer at 85–95 °C, then cooled; plasticiser is incorporated at 5–10 wt% of PVOH solids, and defoamer is added at 0.1–0.3 wt% of the wet adhesive. Starch or dextrin may be co-dissolved at 10–30 wt% of total solids to reduce cost and shorten open time, but borax must be avoided because the fully hydrolysed PVOH chain can gel with borate ions and produce insoluble aggregates in the coating pan. The adhesive is applied by direct gravure, reverse gravure, or slot-die coating at a dry coat weight of 10–20 g/m², then dried in an air-float or arch dryer with web temperature not exceeding 90 °C to prevent skinning. Open time is controlled by the dry film dissolution rate and surface absorption of the paper; the fully hydrolysed grade dissolves more slowly at room temperature than partially hydrolysed grades, which narrows the wet tack window but increases dry blocking resistance. Formulators set the final coated paper moisture to 5–7 % to avoid premature activation in humid storage. Blocking resistance is tested by placing coated-to-coated surfaces under 3–10 kPa at 40 °C and 60 % RH for 24 h; if plasticiser exceeds 10 wt%, blocking increases and the film may transfer to the back side. Wet tack is assessed on bond paper with a defined water volume and a 5 s contact time before lamination. Terminal products include water-moistenable security envelopes, stamps, and wallpaper seam adhesives. Adhesive peel response is measured by ASTM D903-98; published data for this specific 28-99 LA formulation is limited, and lot-specific rheology in the coating pan should be recorded because the high molecular weight creates shear-thinning behaviour that varies with concentration.

When 28-99 LA Replaces Part of the Primary Suspending Agent in VCM Polymerisation

Suspension polymerisation of vinyl chloride monomer in a baffled jacketed stainless steel reactor uses water-soluble PVOH as a stabiliser to control droplet size, porosity, and slurry stability. A partially hydrolysed low-viscosity grade usually serves as the primary suspending agent, while 28-99 LA may be added as a secondary suspending agent to narrow the droplet size distribution and adjust porosity of the resulting S-PVC resin. The total PVOH addition is normally 0.03–0.10 wt% on the water phase, with a primary-to-secondary ratio between 4:1 and 1:1 depending on target K-value and particle morphology. The water-to-monomer ratio is maintained between 1.1:1 and 1.4:1, and the reaction temperature is controlled between 52 °C and 70 °C to set the molecular weight; higher temperatures produce lower K-value resin. Full-hydrolysis secondary PVOH is selected for its stronger interfacial film and limited water absorption; however, secondary addition above 0.05 wt% on water can reduce primary particle coalescence and produce a finer resin with lower plasticiser absorption, which may be acceptable for rigid pipe but undesirable for flexible applications. Production reactors in the 15–40 m³ range are agitated by two-stage impellers at tip speeds adjusted to the reactor diameter and baffle configuration. After polymerisation, the slurry is stripped of residual monomer and the resin is dried to below 0.5 % volatile content. Terminal products include suspension PVC for rigid pipe, profiles, and fittings. Resin quality is graded by ISO 1628-2 for K-value and by ASTM D1755 for general S-PVC classification. Published data for this specific 28-99 LA configuration in VCM suspension polymerisation is limited at the grade-specific level; reactor trials are required to map the primary-to-secondary ratio against particle size distribution and plasticiser absorption because reactor geometry and agitator speed alter the balance.

Textile Warp Size Pickup, Desizing and Reuse Boundaries

In weaving of high-density cotton and polyester-cotton fabric, 28-99 LA is blended into warp size formulations to improve film cohesion and reduce fibre hairiness during shedding. The size is prepared in a jet cooker or conventional size box at 85–90 °C; the PVOH content is typically 10–30 parts per 100 parts starch solids, with a wax or tallow lubricant at 0.5–1.5 wt% on total size solids. The size box solids content is maintained between 8 % and 14 %, and the squeeze rolls are set to give a pickup of 8–15 % on warp yarn weight. The sized warp is dried on multi-cylinder slasher dryers at cylinder surface temperatures of 110–130 °C; if the first drying cylinder exceeds 140 °C, the size film becomes brittle and sheds as dust in the weaving shed. The high degree of hydrolysis of 28-99 LA provides a strong film with low redissolution at ambient loom humidity, which supports weaving efficiency on air-jet and rapier looms. After weaving, desizing is performed in hot water at 70–90 °C, followed by oxidative or enzymatic scouring; the fully hydrolysed grade requires longer wash time because it dissolves more slowly than partially hydrolysed size grades. Terminal fabric products include denim, bed sheeting, and workwear. Sized-yarn and finished-fabric strength is tested by ISO 13934-1 for tensile strength and by ISO 6330 for dimensional stability after washing. Size liquor recovery through ultrafiltration is possible with fully hydrolysed PVOH, but the LA grade reduces inorganic residue build-up in the recovery loop; membrane flux declines when starch-PVOH mixtures exceed 10 % PVOH on total solids due to gel-layer formation, so grade-specific filtration trials are required.

Coated paperboard manufacture uses 28-99 LA as a co-binder in aqueous mineral pigment coating colours where water retention and runnability are controlled under high blade pressure. The coating colour is prepared at 60–70 wt% total solids, containing calcium carbonate or kaolin pigment, synthetic latex binder, and PVOH at 0.5–2.0 parts per 100 parts pigment dry weight. The PVOH is pre-dissolved at 10–15 wt% solids and added to the colour after the latex to avoid shock coagulation. During application by a blade coater running at 600–1500 m/min, the polymer retards water loss into the base sheet by forming a high-viscosity boundary layer at the coating-substrate interface; above 2.0 parts, blade bleeding and high-shear viscosity increase without proportional gain in dry pick strength. The coated board is dried with infrared and air-float dryers to a surface moisture of 4–6 %, then calendered. Terminal products are folding carton board and liquid packaging base board. Surface strength is assessed by ISO 3783, and wet-scuff resistance is evaluated on a wet-abrasion tester according to mill-specific procedures. In closed coating-colour loops, fully hydrolysed PVOH resists biological degradation better than starch but can elevate white-water COD if recovered broke is not neutralised; the LA grade is suitable where extractable ions in the pigment coating would affect food-contact migration testing under FDA 21 CFR 176.170 or European compliance standards for paper and board.