Polyvinyl alcohol coated cellulosic products
A method of manufacture of a coated material is provided. A polyvinyl alcohol polymer, where the polyvinyl alcohol polymer has a degree of hydrolysis of 90% or greater and a melting point in the range of 180° C. to 225° C. is melted on a cellulosic substrate and extruded to form a molten polyvinyl alcohol polymeric film which is then applied directly to the surface of the substrate to form the coated material.
1. A method of manufacture of a coated material comprising the steps of:
providing a cellulosic substrate;
melting a polyvinyl alcohol polymer which includes one or more plasticizers, wherein the polyvinyl alcohol polymer is a blend of two or more homopolymeric polymer grades having low and high respective molecular weights;
each homopolymeric polymer has a degree of hydrolysis of 90 wt % or greater and a melting point in the range of 200° C. to 225° C.;
extruding the melted polyvinyl alcohol polymer to form a molten polyvinyl alcohol polymeric film;
applying the molten polyvinyl alcohol polymeric film directly to the surface of the substrate; and
allowing the molten polyvinyl alcohol polymeric film to solidify on the surface to form a coated material.
2. The method of claim 1 , wherein the molten polyvinyl alcohol polymeric film is applied directly to the surface of the substrate without use of an adhesive or intermediate bonding layer.
3. The method of claim 1 , wherein the polyvinyl alcohol polymer is formed by hydrolysis of polyvinyl acetate homopolymer.
4. The method of claim 1 , wherein the polyvinyl alcohol polymer has a degree of hydrolysis of 93 wt % or greater.
5. The method of claim 4 , wherein the degree of hydrolysis is in the range of 93 wt % to 96 wt %.
6. The method of claim 1 , wherein the one or more plasticizers are selected from the following plasticizers and mixtures thereof:
(a) sugar alcohols selected from the group consisting of: diglycerol, triglycerol, fructose, ribose, xylose, D-mannitol, triacetin, and mixtures thereof;
(b) polyols selected from the group consisting of: pentaerythritol, dipentaerythritol, and mixtures thereof;
(c) diols selected from the group consisting of: methyl pentanediol, 1,2-propanediol, 1,4-butanediol, 2-hydroxy-1,3-propanediol, 3-methyl-1,3-butanediol, 3,3-dimethyl-,2-butanediol, and mixtures thereof;
(d) glycols selected from the group consisting of: polyethylene glycol 300, polyethylene glycol 400, alkoxylated polyethylene glycol, and mixtures thereof; and
(e) caprolactam, cyclic trimethylolpropane formal, rosin esters, euricamide, and mixtures thereof.
7. The method of claim 1 , wherein the cellulosic substrate is paper, board or card.
8. The method of claim 1 , wherein the blend comprises a first grade having a molecular weight in the range of 13,000 to 27,000 and a degree of polymerization of 300 to 600 and a second grade having a molecular weight in the range of 107,000 to 120,000 and a degree of polymerization of 2,400 to 2,600.
9. The method of claim 1 , wherein the polyvinyl alcohol polymer includes one or more reactive stabilizers selected from the group consisting of:
calcium stearate, stearic acid, sodium stearate, potassium oleate, potassium sorbate, sodium benzoate and mixtures thereof.
10. The method of claim 1 , wherein a reduced viscosity is maintained when shear is applied to the molten polyvinyl alcohol polymer, the reduced viscosity being maintained if the shear is applied for a period up to one hour or longer.
11. The method of claim 1 , wherein the viscosity of the molten polyvinyl alcohol polymer decreases with increasing shear rate from a viscosity at a shear rate of 80l/s to a viscosity at a shear rate of 1000l/s, the viscosities being measured at steady states following application of shear to the molten polyvinyl alcohol polymer for up to one hour.
12. The method of claim 1 , wherein the polyvinyl alcohol polymer is pseudoplastic.
13. The method of claim 1 , wherein the polyvinyl alcohol polymer has a degree of hydrolysis of 95 wt % or greater.
14. The method of claim 8 , wherein the two or more polyvinyl alcohol polymer grades have the same hydrolysis degree (HD) value.
15. The method of claim 1 , wherein the one or more plasticizers are diglycerol, triglycerol, xylose, D-mannitol, triacetin, dipentaerythritol, 1,4-butanediol, 3,3-dimethyl-,2-butanediol, caprolactam and mixtures thereof.
16. The method of claim 1 , wherein the polyvinyl alcohol polymer dissolves in 10 minutes in water having a temperature from about 30° C. to about 60° C. and 100% of the undissolved cellulose fibers are released from the coated material.
17. The method of claim 16 , wherein the coated material is processable in a conventional paper mill.
18. The method of claim 9 , wherein the polyvinyl alcohol polymer includes sodium benzoate.