Method of heat-treating packaged product and heat-treated packaged product

Abstract

A packaged product formed by enclosing a content material, such as food or beverage, sanitary products or medical products, within a packaging material including at least a layer of hydrophilic resin, is heat-treated with hot water for, e.g., boil sterilization or retort sterilization. The hot water is caused to contain a water-soluble compound in an amount substantially exceeding a level contained in tap water, whereby it becomes possible to suppress the opalescence of the packaging material causing inferior appearance or transparency and leading to a lowering in gas-barrier property, which has been problematic in the conventional boil or retort hot water treatment.

1 - 24 . (canceled)  
     
     
         25 . A heat-treating method for a packaging product, comprising: 
 providing a packaging product formed by enclosing a content material within a packaging material comprising at least a layer of hydrophilic resin, and    heat-treating the packaging product with hot water,    wherein the hot water is caused to contain a water-soluble compound.    
     
     
         26 . A heat-treating method according to  claim 25 , wherein the hot water has a temperature of 60-100° C. to effect a boiling heat-treatment.  
     
     
         27 . A heat-treating method according to  claim 25 , wherein the hot water has a temperature exceeding 100° C. to effect a retort heat-treatment.  
     
     
         28 . A heat-treating method according to  claim 25 , wherein the hot water contains the water-soluble compound at a concentration exceeding 0.1 wt. %.  
     
     
         29 . A heat-treating method according to  claim 25 , wherein the hot water contains the water-soluble compound at a concentration of at least 1 wt. %.  
     
     
         30 . A heat-treating method according to  claim 25 , wherein the water-soluble compound is an inorganic electrolyte.  
     
     
         31 . A heat-treating method according to  claim 30 , wherein the water-soluble compound is a water-soluble inorganic salt.  
     
     
         32 . A heat-treating method according to  claim 31 , wherein the water-soluble compound is a chloride selected from the group consisting of sodium chloride, magnesium chloride, and potassium chloride.  
     
     
         33 . A heat-treating method according to  claim 32 , wherein the water-soluble compound is sodium chloride.  
     
     
         34 . A heat-treating method according to  claim 25 , wherein the water-soluble compound is a water-soluble organic compound.  
     
     
         35 . A heat-treating method according to  claim 34 , wherein the water-soluble compound is a water-soluble alcohol.  
     
     
         36 . A heat-treating method according to  claim 25 , wherein the hydrophilic resin layer is a gas-barrier resin layer.  
     
     
         37 . A heat-treating method according to  claim 36 , wherein the gas-barrier resin is selected from the group consisting of ethylene-vinyl alcohol copolymer, polyamide (co-)polymers, and aliphatic ester (co-)polymers.  
     
     
         38 . A heat-treating method according to  claim 37 , wherein the gas-barrier resin is selected from the group consisting ethylene-vinyl alcohol copolymer, polymetaxylylene adipamide and glycolic acid (co-)polymer.  
     
     
         39 . A heat-treating method according to  claim 25 , wherein the packaging material has a multi-layer structure.  
     
     
         40 . A heat-treating method according to  claim 39 , wherein the hydrophilic resin layer is disposed as a surface layer contacting the hot water of the packaging material.  
     
     
         41 . A heat-treating method according to  claim 39 , wherein the hydrophilic resin layer is disposed as an inner layer not directly contacting the hot water of the packaging material.  
     
     
         42 . A heat-treating method according to  claim 41 , wherein the gas-barrier resin is glycolic acid (co-)polymer.  
     
     
         43 . A packaged product, which has been heat-treated by a heat-treating method according to  claim 25 .  
     
     
         44 . A packaged product according to  claim 43 , wherein the heat-treated packaging material has a haze below 20%.  
     
     
         45 . A heat-treated packaged product, comprising a heat-treated packaging material having a multi-layer structure including an inner layer of a hydrophilic gas-barrier resin layer selected from the group consisting of ethylene-vinyl alcohol copolymer and glycolic acid (co-)polymer, and a content material enclosed within the packaging material, wherein the heat-treated packaging material has a haze below 20%.  
     
     
         46 . A packaged product according to  claim 45 , wherein the hydrophilic gas-barrier resin is ethylene-vinyl alcohol copolymer.  
     
     
         47 . A packaged product according to  claim 45 , wherein the hydrophilic gas-barrier resin is glycolic acid (co-)polymer.  
     
     
         48 . A packaged product according to  claim 43 , wherein the packaged material has been subjected to a heat-shrinking treatment during the heat treatment.