KURARAY POVAL 28-98

Polyvinyl alcohol (PVOH) having varying degree of polymerization and hydrolysis.

Kuraray Poval™ resin as a binder in textile sizes

A binder in sizes is based on its good penetration capacity and good adhesion properties on all types of fibrous material. The excellent film characteristics of Kuraray Poval™ resin like high cohesion and toughness, low electrostatic charging and redissolving capacity of the dried film in water complete the characterization of this polymer as a suitable agent for this purpose

The characteristics of PVOH make it well suited for an extensive range of applications in products that individuals use every day. From an emulsion polymerization aid to a binder for pigments in paper applications, the versatility of PVOH is widespread.

Kuraray Poval™ resin as a versatile auxiliary aid in paper applications

Due to its broad property profile, Kuraray Poval™ resin is frequently used as a co-binder in paper coatings. The particular suitability of Kuraray Poval™ resin in pigmented coatings is based on:

• Its outstanding carrier properties of optical brightening agents
• Its excellent colloidal protection becoming effective in high solids pigment formulations which establishes a smooth viscosity profile
• Its good water retention in coating colors
• Its high binding strength in paper coatings which can be related to polymer cohesion as well as to good adhesion to the fiber and the pigment particles, respectively

Low molecular weight Kuraray Poval™ grades such as Kuraray Poval™ resin 6-98 are the preferred polyvinyl alcohols to be used in paper coatings. Kuraray Poval™ resin possesses remarkable barrier properties. Due to its insolubility in most organic solvents, surfaces treated with Kuraray Poval™ resin repel hydrophobic products such as oil, grease, and fat. Furthermore, Kuraray Poval™ resin displays excellent mechanical strength properties if applied as a film on paper or paperboard.

Therefore, it fits well as a surface sizing agent. Many special paper grades are produced using Kuraray Poval™, such as:

• Silicon base paper, to be used as release paper for PSA labels
• Banknote paper and grades with high folding endurance
• Thermoreactive paper for barcode labels or facsimile machines
• Film casting (release) paper
• Ink-jet paper

Preparation of PVOH Solutions

In the adhesives sector, PVOH is processed as an aqueous solution as it is in most other fields of application. The solutions should be prepared in corrosion-resistant vessels. In the case of Fully and Medium hydrolyzed PVOH, the PVOH is sprinkled into cold water during stirring and heated to 90 - 95°C in a water bath or by the use of live steam. In the case of Partially hydrolyzed PVOH, the PVOH is sprinkled into cold water during stirring and heated to 70 - 95°C in a water bath or by the use of live steam. The solution should be stirred during cooling to prevent skin formation.

The speed of dissolution increases with increasing temperature. For both partially and fully hydrolyzed PVOH grades the speed of dissolution decreases with increasing molecule size (increasing viscosity of the 4 % aqueous solution). The dissolving process is also made more difficult when there is a transition to higher concentrations. As a result, even more highly concentrated PVOH solution, (e.g. 30 % solution of Kuraray Poval™ 5-88), should be produced at temperatures of 90–95°C. Polyvinyl alcohol solutions may produce foam during stirring or transporting in pipelines, but this can be largely prevented by using a suitable stirrer design such as a low-speed anchor stirrer or by avoiding steep downward gradients in the pipelines.

Suitable defoamers are offered by numerous suppliers such as Dow Corning, Air Products and Chemicals, Inc., Emerald Performance Materials, Munzing Chemie GmbH, etc. Please check regulatory compliance if the application requires such status. Polyvinyl alcohol solutions which have been stored for lengthy periods may show increases in viscosity. This is especially true of fully hydrolyzed grades in high concentrations and at low temperature. The original viscosity can be restored by heating and stirring.

Polyvinyl alcohols are water-soluble polymers manufactured by alcoholysis of polyvinyl acetate. The properties of the various grades are mainly governed by the molecular weight and the remaining content of the acetyl groups.

Under certain conditions, aqueous solution PVOH can be attacked by micro-organisms. The main organisms that can reproduce in the acidic pH range are the fission fungi, whilst bacteria grow most readily in a neutral to weakly alkaline medium. The PVOH solutions can be preserved from any microorganism attack by the addition of preservatives. Suitable preservatives are offered by numerous suppliers such as Dow Chemical, Bayer Chemicals, Troy Corporation, Thor Specialties, Inc. etc. The dosage depends on the concentration of the solution, the storage temperature and the nature and intensity of the infection. Quantities of about 0.01 - 0.2% by weight preservative, relative to the PVOH solution, are generally sufficient. Compatibility and efficiency must be tested. Information on the quantity to be used is available directly from the suppliers.

It is advisable for the PVOH solution to be prepared and stored in clean containers. Considering the resistance that is shown by some micro-organisms to the preservatives employed, the dissolving vessel in particular, together with the filling equipment (pipes, valves, tubing, etc.), needs to be kept clean. Any skins or incrustations should be removed. In the event of complications, the possibility of changing to a different preservative must be considered.

Kuraray Poval™ resin can be stored for an unlimited period of time under appropriate conditions that is in its original packs in closed, dry rooms, at room temperature. Kuraray would recommend that our product is used within 12 months from the shipment date as given on the certificate of analysis.