Process for producing newsprint

Claim 1

A method for producing a high quality newsprint pulp from wood or vegetable fibrous material comprising: (a) providing a quantity of said fibrous material in a form suitable for input into a digester; (b) (i) conveying at least forty percent by weight of said quantity of fibrous material to a thermochemical digester and contacting said fibrous material with an alkaline cooking liquor whereby lignin is removed from said fibrous material and said fibrous components; (ii) after digesting said fiber for from 0.1 to 1 hour at 140° C. to 190° C., refining the digested fiber at above 100° C.; (iii) rapidly reducing the pressure on said digested and refined fibers to approximately ambient pressure and washing and screening said fiber to remove pulping chemicals and dirt and other foreign fragments therefrom; and (iv) contacting said washed and screened fibers with a bleachant for a time sufficient to raise the GE brightness of said fibers to greater than about 60; (c) (i) conveying the remainder of said quantity of fibrous material to a thermomechanical digester which consists of a first section and a second section, said sections being separated by a refiner; (ii) contacting said fibrous material within the first section, of said thermomechanical digester with steam at a pressure greater than about 2 kg/sq. cm and mechanically working said fiber in said section of the digester to partially reduce said fibrous material to its fiber components; (iii) conveying the fibrous material from the first section of said digester to a refiner and refining said fibrous material; (iv) contacting the refined fiber in a second section of said thermomechanical digester with steam at a pressure of less than about 2 kg/cm 2 , whereby said fibrous material is substantially reduced to its fiber components; (v) refining the digested fiber and rapidly reducing the pressure on the digested fiber to approximately ambient pressure; and (vi) refining said digested and elevated pressure refined fibers at ambient pressure; and washing and screening the refined fibers to remove dirt and large fiber fragments therefrom; (d) intermixing the bleached fiber from thermochemical digestion with the fiber from thermomechanical digestion; and; (e) producing a newsprint paper from such intermixed fibers.

Claim 2

A method for producing a high quality newsprint pulp from wood or vegetable fibrous material comprising: (a) providing a quantity of said fibrous material in a form suitable for input into a digester; (b) (i) conveying at least forty percent by weight of said quantity of fibrous material to a thermochemical digester and contacting said fibrous material with an alkaline cooking liquor whereby lignin is removed from said fibrous material and said fibrous components; (ii) after digesting said fiber for from 0.1 to 1 hour at 140° C. to 190° C., refining the digested fiber at above 100° C.; (iii) rapidly reducing the pressure on said digested and refined fibers to approximately ambient pressure and washing and screening said fiber to remove pulping chemicals and dirt and other foreign fragments therefrom; and (iv) contacting said washed and screened fibers with a bleachant for a time sufficient to raise the GE brightness of said fibers to greater than about 60; (c) (i) conveying the remainder of said quantity of fibrous material to a thermomechanical digester which consists of a first section and a second section, said sections being separated by a refiner; (ii) contacting said fibrous material within the first section, of said thermomechanical digester with steam at a pressure greater than about 2 kg/sq. cm and mechanically working said fiber in said section of the digester to partially reduce said fibrous material to its fiber components; (iii) conveying the fibrous material from the first section of said digester to a refiner and refining said fibrous material; (iv) contacting the refined fiber in a second section of said thermomechanical digester with steam at a pressure of less than about 2 kg/cm 2 , whereby said fibrous material is substantially reduced to its fiber components; (v) refining the digested fiber and rapidly reducing the pressure on the digested fiber to approximately ambient pressure; and (vi) refining said digested and elevated pressure refined fibers at ambient pressure; and washing and screening the refined fibers to remove dirt and large fiber fragments therefrom; (d) intermixing the bleached fiber from thermochemical digestion with the fiber from thermomechanical digestion; and; (e) producing a newsprint paper from such intermixed fibers.