KURARAY POVAL 20-98 M

Kuraray POVAL 20-98 M is supplied as a fully hydrolyzed polyvinyl alcohol powder with a 4% aqueous solution viscosity of 20.0–22.0 mPa·s at 20 °C and a degree of hydrolysis of 98.0–99.0 mol% measured in accordance with JIS K6726. In paper surface sizing and pigment coating, the grade is used where low cold-water sensitivity and high dry pick resistance must be maintained on lithographic and packaging grades. The resin is dispersed in cold water at ambient temperature, then heated to 90–95 °C for 30–45 min in a jet cooker or agitated jacketed tank to complete dissolution; the solution is cooled to 55–65 °C and held. Typical surface size formulations add 10–30 dry parts of 20-98 M per 100 dry parts of total size solids, with the balance oxidized starch or a starch/polyacrylamide blend, depending on the target Hercules size test response. Application on a metering size press or rod-metering film press deposits 0.8–2.5 g/m² per side. Sizing response is quantified by TAPPI T 530 on the Hercules scale and water absorption by ISO 535 Cobb testing. The fully hydrolyzed backbone reduces the binder contribution to Cobb value and improves IGT dry pick strength relative to partially hydrolyzed 88 mol% grades. Terminal products include recycled white-top liner, folding boxboard, and sheet-fed offset packaging. Food-contact compliance is established under FDA 21 CFR 176.170 for aqueous and fatty food-contact paper and FDA 21 CFR 176.180 for dry food-contact paper; the substance is registered under REACH Regulation 1907/2006. Process boundaries include foam in high-shear hold tanks using centrifugal size pumps with recirculation above 15 tank turnovers/h, which requires a defoamer dose of 0.05–0.15 wt% based on wet size solution. The polymer is incompatible with borate-containing additives, which cause gelation; blending pH should remain above 5.0.

What Controls Remoistenable Adhesive Wet Tack on High-Speed Envelope Converting Lines?

Remoistenable gum systems formulated with Kuraray POVAL 20-98 M are processed as aqueous solutions at 25–45 wt% dry solids and applied to envelope flaps, paper sacks, labels, and stamps by engraved roll or transfer coater. The fully hydrolyzed grade yields a dry film that remains non-tacky at ambient humidity and develops adhesion only after controlled remoistening; this behavior reduces feed table blocking on high-speed window-patching lines. A typical formulation combines 100 dry parts of 20-98 M with 30–60 dry parts of dextrin or thin-boiling starch, 5–15 phr of glycerol or sorbitol as plasticizer, and 0.1–0.3 phr of defoamer. The adhesive is cooked at 85–95 °C and applied at 50–65 °C through an engraved coater or kiss coater onto gummed areas. Wet coat weight ranges from 5–20 g/m², followed by forced-air drying at 60–90 °C to residual moisture below 5.0 mass%. Peel adhesion after remoistening with 10–15 g/m² of water is evaluated by ASTM D903. Blocking resistance is screened by stacking finished envelopes at 40 °C and 70 % relative humidity for 72 h under 5–10 kPa load. The main operational boundary is humidity exposure above 70 %; blocking may occur unless anti-block additives such as calcium stearate at 0.5–1.0 phr are added. Borax or boric acid must not be added above trace amounts because these crosslink the fully hydrolyzed PVOH and produce irreversible gelation in the holding tank. The dried adhesive is compliant with FDA 21 CFR 175.105 for indirect food-contact adhesives when applied under good manufacturing practice. Terminal articles include self-seal envelopes, remoistenable wallpaper borders, and high-speed insertion mailers.

In aqueous ceramic tape casting, Kuraray POVAL 20-98 M functions as a fully hydrolyzed binder for alumina, zirconia, barium titanate, and low-temperature co-fired ceramic formulations. A binder solution is prepared separately at 10–15 wt% solids by heating to 90 °C, then cooled before addition to the slip to avoid flocculation. The ceramic slip is milled with deionized water, ammonium polyacrylate dispersant at 0.5–1.5 wt% based on ceramic powder, defoamer at 0.1–0.3 wt%, and plasticizer such as PEG 400 at 10–30 wt% based on polymer. Binder addition is expressed as 2–6 dry parts per 100 dry parts ceramic powder; the final slip solids are typically 55–75 wt%. Viscosity is controlled to 1500–4000 mPa·s at 10 s⁻¹ using a cone-plate rotational rheometer. After vacuum de-airing at 20–50 kPa for 10–20 min, the slip is cast onto a polyethylene terephthalate carrier with a doctor blade gap of 0.25–0.60 mm. Carrier speed is set between 0.3 and 1.5 m/min, and drying is carried out in a segmented tunnel at 50–80 °C until residual moisture falls below 1.0 mass%. Green tapes of 0.10–0.35 mm thickness are laminated at 10–20 MPa and 70 °C for multilayer builds. Binder burnout in air uses a ramp rate no greater than 0.5 °C/min through 550 °C, with isothermal holds at 150 °C, 350 °C, and 600 °C to prevent blistering and residual carbon defects. Resin ash is specified below 0.5 mass% after incineration at 900 °C according to ISO 3451-1. Sintered substrates are checked for water absorption and apparent porosity under ASTM C373. The grade is suitable for multilayer ceramic capacitor green sheet, LTCC modules, oxygen sensor substrates, and ceramic heater plates. Operational limits include slurry pot life of 24–48 h without biocide addition, because PVOH solutions support microbial growth; processing above 48 h requires a preservative compatible with the ceramic dispersant. Binder contents above 6 dry parts per 100 dry parts powder increase green strength but lengthen burnout and raise residual carbon risk in reducing atmospheres.

Fully Hydrolyzed PVOH Feedstock Provides the Backbone for Butyralization

The butyralization reactor charge is prepared by dissolving Kuraray POVAL 20-98 M in demineralized water at 90–95 °C to 8–12 wt%, then cooling to 20–40 °C before catalyst addition. Butyraldehyde is added at 0.7–0.9 mol per mole of vinyl alcohol unit, and hydrochloric or sulfuric acid drops the pH to 1.5–2.5. Precipitation of polyvinyl butyral occurs as the reaction proceeds through 3–6 h; the precipitated resin is washed repeatedly until residual ionic impurities are below lot specification by ion chromatography. The 20-98 M grade at 20.0–22.0 mPa·s delivers a lower molecular weight fully hydrolyzed backbone than higher-viscosity PVOH grades, which reduces melt viscosity during subsequent sheet extrusion and permits faster line speeds on 0.76 mm and 1.52 mm interlayer calenders. Typical PVB resin after butyralization contains 75–80 mol% butyral units, 15–20 mol% residual hydroxyl, and less than 1.5 mol% residual acetate. Compounding with plasticizer at 25–40 phr is followed by extrusion through a flat die at 180–220 °C. Laminated glass made from the interlayer is tested under ISO 12543 and, for automotive glazing, ECE R43. The terminal product is safety glass for architectural and automotive applications. Processing boundaries are set by the relationship between residual hydroxyl and adhesion: hydroxyl content below 15 mol% reduces glass adhesion in pummel testing, while content above 20 mol% increases moisture sensitivity of the interlayer. The use of a fully hydrolyzed PVOH feedstock rather than an 88 mol% grade raises crystal density in the dry polymer, requiring the dissolution stage to be held at or above 90 °C; incomplete dissolution leaves undissolved particles that appear as optical defects in the cast interlayer. Compliance for the final interlayer is evaluated under ECE R43 for optical quality and adhesion performance, and the PVOH feedstock itself is registered under REACH Regulation 1907/2006.

When Cementitious Tile Adhesives Need Open Time Without Set Retardation

Dry-mix formulations containing 0.2–0.8 wt% Kuraray POVAL 20-98 M are used in cement-based tile adhesives, skim coats, and exterior insulation and finishing system base coats to increase water retention and improve adhesion to low-absorptive substrates. The powder is dry-blended with cement, sand graded between 0.1 and 1.0 mm, and cellulose ether in a horizontal ribbon mixer for 5–10 min. The fully hydrolyzed PVOH does not dissolve completely in cold water at 20 °C, but disperses under alkaline cement hydration and high-shear mixing; this delayed dissolution mechanism extends open time without the immediate viscosity spike associated with fully cold-water-soluble grades. Mixed mortar is applied with a 6 mm × 6 mm notched trowel and tested according to EN 1348 for tensile adhesion after 28 days of standard storage and after water immersion. Formulations are classified under EN 12004 for cementitious adhesives. The PVOH addition contributes to pot life and slip resistance, but the operational ceiling is 1.0 wt%; above this level set retardation and air entrainment increase, and compressive strength measured by EN 196-1 may fall below the required class. The grade is used together with methyl hydroxyethyl cellulose because PVOH alone does not provide sufficient water retention at low mortar thickness. The main process boundary is application below 5 °C, where dissolution of the fully hydrolyzed grade is too low to develop full binder contribution. The final cementitious products include C2TE and C2TES1 tile adhesives for porcelain tile installation, gypsum-based repair compounds, and polymer-modified cement slurries for floor leveling.

On shuttleless weaving lines running air-jet or rapier looms, Kuraray POVAL 20-98 M is applied as a warp size for spun cotton, polyester/cotton, and viscose warps where high abrasion resistance is required at low size add-on. Size box temperature is maintained at 85–95 °C, and the size liquor is made down at 8–15 wt% solids, either as a single-component size or blended with starch or acrylic co-binder. The solids pick-up on warp yarn is controlled to 8–12 dry mass% by squeeze roller pressure and slasher speed. Dry-can temperatures are staged from 120 °C to 90 °C to prevent skinning and to maintain residual moisture at 6–8 mass% before leasing. Sized yarn tensile properties are measured by ASTM D2256, and loom efficiency is monitored on high-speed air-jet installations at insertion rates above 1000 m/min. The fully hydrolyzed structure produces a tough, crystalline size film with low cold-water solubility, so removal requires desizing at 80–95 °C in an alkaline bath containing sodium persulfate or hydrogen peroxide; PVA is not broken down by amylase alone. Residual PVOH on fabric is confirmed by iodine-boric acid color reaction before dyeing because any residual film can interfere with reactive dye diffusion and cause crack marks on sanforizing. The grade is applicable to indigo denim face yarns, filament polyester/cotton shirtings, and industrial canvas. The operational boundary is the high desizing temperature; plants without pressurized wash boxes or multi-box open-width ranges may retain PVOH residues, which appear as stiff hand after finishing. Occupational exposure and effluent controls follow the REACH Regulation 1907/2006 and the Zero Discharge of Hazardous Chemicals Manufacturing Restricted Substances List; PVOH is not restricted but conventional desizing effluent must be treated for high COD before discharge.