Pulp Bleaching Processes

Abstract

The present invention aims to further advance the acid treatment or irradiation technology for pulp to develop a bleaching process using smaller amounts of chlorine chemicals with higher efficiency as compared with conventional bleaching processes. It also aims to provide an excellent high brightness pulp having a low environmental impact and no discoloration as well as a paper containing it. The present invention provides a chlorine-free bleaching process with very high efficiency by irradiating a pulp washed after an acid treatment with UV light and/or visible light at a wavelength of 100-400 nm under alkaline conditions, preferably in a pH range of 10-13. The acid treatment can be performed under conditions of pH 1-6 and a temperature of 80° C. or more. The irradiation treatment can be performed in the presence of at least one compound selected from the group consisting of reducing agents, peroxides, and hydrogen-donating organic compounds. The present invention also provides a high brightness chemical pulp having an ISO brightness of 88% or more and a brightness loss of 1.0% or less in a specific fading test.

1 . A pulp bleaching process characterized in that a pulp washed after an acid treatment is irradiated with UV light and/or visible light at a wavelength of 100-400 nm under alkaline conditions.  
   
   
       2 . The pulp bleaching process of  claim 1  characterized in that the alkaline conditions comprise a pH range of 10-13.  
   
   
       3 . The pulp bleaching process of  claim 1  characterized in that the acid treatment is performed under conditions of pH 1-6 and a temperature of 80° C. or more.  
   
   
       4 . The pulp bleaching process of  claim 1  characterized in that the acid treatment is performed in the presence of ozone under conditions of pH 1.0-8.0 and a temperature of 25-95° C.  
   
   
       5 . The pulp bleaching process of  claim 1  characterized in that the irradiation treatment is performed in the presence of at least one compound selected from the group consisting of reducing agents, peroxides, and hydrogen-donating organic compounds.  
   
   
       6 . The pulp bleaching process of  claim 1  characterized in that the irradiation source of the UV light and/or visible light consists of multiple light sources having different wavelength characteristics.  
   
   
       7 . The pulp bleaching process of  claim 1  characterized in that the irradiation treatment is repeated multiple times.  
   
   
       8 . A pulp bleaching process characterized in that a pulp washed after an acid treatment is irradiated with UV light and/or visible light at a wavelength of 100-400 nm in the presence of ozone.  
   
   
       9 . The pulp bleaching process of  claim 8  characterized in that the irradiation treatment with UV light and/or visible light is performed under acidic conditions of pH 2-4 or under alkaline conditions of pH 10-13.  
   
   
       10 . The pulp bleaching process of  claim 8  characterized in that the acid treatment is performed under conditions of pH 1-6 and a temperature of 80-180° C.  
   
   
       11 . The pulp bleaching process of  claim 8  characterized in that the acid treatment is performed in the presence of ozone under conditions of pH 1-8 and a temperature of temperature 25-95° C.  
   
   
       12 . The pulp bleaching process of  claim 8  characterized in that the ozone is generated by irradiating air or oxygen or a mixture thereof with UV light.  
   
   
       13 . The pulp bleaching process of  claim 8  characterized in that the ozone concentration during the irradiation treatment is 0.5-100 ppm.  
   
   
       14 . A pulp bleacher characterized in that air or oxygen or a mixture thereof is supplied to the surroundings of an irradiation source of UV light and/or visible light to generate ozone and a gas containing the ozone is fed to a pulp.  
   
   
       15 . A pulp bleacher comprising an ozone-generating chamber having an irradiation source for emitting UV light and/or visible light therein and a pulp slurry chamber, wherein the ozone-generating chamber has a gas injection port and a discharge port, and the discharge port communicates with the pulp slurry chamber.  
   
   
       16 . A totally chlorine-free (TCF) bleaching process for chemical pulp characterized in that an oxygen-delignified pulp is acid-treated and then bleached by a bleaching process used in totally chlorine-free bleaching, and the resulting pulp is further subjected to a light bleaching treatment with UV light and/or visible light at a wavelength of 100-400 nm under alkaline conditions, followed by alkaline hydrogen peroxide bleaching.  
   
   
       17 . A totally chlorine-free bleaching process for chemical pulp characterized in that an oxygen-delignified pulp is acid-treated and then bleached by a bleaching process used in normal TCF bleaching to an ISO brightness of 70-75%, and the resulting pulp is further subjected to a light bleaching treatment with UV light and/or visible light at a wavelength of 100-400 nm under alkaline conditions to an ISO brightness of 75-80%, followed by alkaline hydrogen peroxide bleaching to give a pulp having an ISO brightness of 84% or more.  
   
   
       18 . The bleaching process for chemical pulp of  claim 16  characterized in that the light bleaching treatment is performed in a pH range of 10-13.  
   
   
       19 . The bleaching process for chemical pulp of  claim 16  characterized in that the acid treatment is performed under conditions of pH 1-6 and a temperature of 80° C. or more.  
   
   
       20 . The bleaching process for chemical pulp of  claim 16  characterized in that the light bleaching treatment is performed in the presence of at least one compound selected from the group consisting of oxidizing agents, reducing agents, and peroxides.  
   
   
       21 . A high brightness chemical pulp having an ISO brightness of 88% or more and a brightness loss of 1.0% or less in the following fading test: a hand-made paper is prepared according to JIS P 8222 and irradiated with a xenon lamp at an intensity of 67 W/m 2  for 30 minutes in an atmosphere at 30° C. according to fading test method B of J. TAPPI No. 21 Paper and Paperboard (using a xenon arc lamp light fastness tester) and then the ISO brightness is measured and a loss from the ISO brightness before treatment is determined.  
   
   
       22 . The high brightness chemical pulp of  claim 21 , which has been treated with UV light and/or visible light and has an ISO brightness of 88% or more.  
   
   
       23 . A paper containing the high brightness chemical pulp of  claim 21 .  
   
   
       24 . A process for preparing a high brightness chemical pulp characterized in that a bleached chemical pulp is treated with UV light and/or visible light.  
   
   
       25 . A process for preparing a high brightness chemical pulp characterized in that a bleached chemical pulp having an ISO brightness of 80% or more is treated with UV light and/or visible light to an ISO brightness of 88% or more.  
   
   
       26 . The bleaching process for chemical pulp of  claim 17  characterized in that the light bleaching treatment is performed in a pH range of 10-13.  
   
   
       27 . The bleaching process for chemical pulp of  claim 17  characterized in that the acid treatment is performed under conditions of pH 1-6 and a temperature of 80° C. or more.  
   
   
       28 . The bleaching process for chemical pulp of  claim 17  characterized in that the light bleaching treatment is performed in the presence of at least one compound selected from the group consisting of oxidizing agents, reducing agents, and peroxides.