Water-soluble film

Abstract

A film-forming composition made from a mixture of PVOH, chitosan, an alkali metal or ammonium bisulfite or metabisulfite, and optional ingredients such as plasticizers, antioxidants, UV stabilizers, surfactants, crosslinking agents, lubricants, and extenders, is disclosed. Also disclosed are a method of making a film from the composition, a resulting film, and a packet made from the film and containing a cleaning composition such as a rinse additive. The composition can be formulated to yield an article such as a film which is soluble only below a predetermined pH threshold.

1 . A water-soluble film comprising a mixture of PVOH, chitosan present in an amount up to 20 wt %, and an alkali metal or ammonium bisulfite or metabisulfite. 
     
     
         2 . The film of  claim 1 , wherein the alkali metal or ammonium bisulfite or metabisulfite comprises sodium bisulfite. 
     
     
         3 . The film of  claim 1 , wherein the alkali metal or ammonium bisulfite or metabisulfite is present in an amount in a range of 0.01 wt % to 1 wt %. 
     
     
         4 . The film of  claim 3 , wherein the alkali metal or ammonium bisulfite or metabisulfite is present in an amount in a range of 0.02 wt % to 0.25 wt %. 
     
     
         5 . The film according to  claim 1 , wherein the PVOH has a degree of hydrolysis of greater than 88%. 
     
     
         6 . The film according to  claim 5 , wherein the PVOH has a degree of hydrolysis in a range of 92% to 98%. 
     
     
         7 . The film according to  claim 1 , wherein the chitosan is present in an amount in a range of about 1 wt % to about 20 wt %. 
     
     
         8 . The film according to  claim 1 , wherein the chitosan has a degree of acetylation in a range of about 55% to about 65%. 
     
     
         9 . The film according  claim 8 , wherein the chitosan has a degree of acetylation in a range of about 60% to about 65%. 
     
     
         10 . The film according to  claim 1 , wherein the film is soluble in water having a pH up to about 9.3. 
     
     
         11 . The film according to  claim 1 , wherein the film is insoluble in water having a pH greater than about 9.3. 
     
     
         12 . The film according to  claim 1 , further comprising a plasticizer. 
     
     
         13 . The film of  claim 12 , wherein the plasticizer is present in a range of about 10 wt % to about 20 wt %. 
     
     
         14 . The film of  claim 12 , wherein the plasticizer comprises glycerin. 
     
     
         15 . A water-soluble film comprising 50 wt % to 90 wt % PVOH having a degree of hydrolysis in a range of 92% to 98%, 1 wt % to 20 wt % chitosan having a degree of acetylation in a range of about 60% to 65%, and 0.01 wt % to 1 wt % sodium bisulfite, wherein the film is insoluble in water having a pH about 9.3 or greater. 
     
     
         16 . A water-soluble film comprising a mixture of PVOH, chitosan and an alkali metal or ammonium bisulfite or metabisulfite wherein the weight ratio of PVOH to chitosan in a range of about 12:1 to about 3:1 
     
     
         17 . A sealed packet comprising the film of  claim 1 . 
     
     
         18 . A method of making a water-soluble film, comprising the steps of:
 preparing a solution including PVOH polymer and chitosan;   adding an alkali metal or ammonium bisulfite or metabisulfite, casting the solution;   and drying off solvent to thereby obtain a water-soluble polymer film.   
     
     
         19 . The method of  claim 18 , wherein the solution of PVOH and chitosan is prepared by
 slurrying a PVOH polymer in a dilute, cold aqueous solution of chitosan;   adding any optional ingredients to the slurry, including plasticizers, antioxidants, surfactants, lubricants, and extenders; and   heating the slurry with agitation to thereby solubilize the PVOH.   
     
     
         20 . The method of  claim 18 , further comprising delaying addition of the alkali metal or ammonium bisulfite or metabisulfite to the solution including PVOH polymer and chitosan for a time sufficient to increase the wet strength of the resulting film. 
     
     
         21 . The method of  claim 20 , wherein said time is at least two hours. 
     
     
         22 . A film made by the method of  claim 18 .