Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F11/00—Processes for making continuous lengths of paper, or of cardboard, or of wet web for fibre board production, on paper-making machines
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/14—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by function or properties in or on the paper
  • D21H21/18—Reinforcing agents
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H25/00—After-treatment of paper not provided for in groups D21H17/00 - D21H23/00
  • D21H25/04—Physical treatment, e.g. heating, irradiating
  • D21H25/06—Physical treatment, e.g. heating, irradiating of impregnated or coated paper
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
  • D21H27/30—Multi-ply
  • D21H27/40—Multi-ply at least one of the sheets being non-planar, e.g. crêped
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H5/00—Special paper or cardboard not otherwise provided for
  • D21H5/12—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials
  • D21H5/1272—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials of fibres which can be physically or chemically modified during or after web formation
  • D21H5/129—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials of fibres which can be physically or chemically modified during or after web formation by thermal treatment

Definitions

• This invention relates to the art of papermaking, particularly to treating of formed paper product with heat and subsequent rewetting to improve its properties, including dry and wet stiffness, wet tensile strength and opacity.
• Quantifiable paper properties include: dry and wet tensile strength, folding endurance, stiffness, compressive strength, and opacity, among others. Which qualities should desirably be enhanced depends upon the intended application of the product. In the case of mild carton board, for example, stiffness is of utmost importance. Linerboard has three qualities of particular interest, namely wet strength, folding endurance, and high humidity compression strength.
• wet strength means wet tensile strength as measured by America Society for Testing and Materials (ASTM) Standard D829-48.
• Folding endurance is defined as the number of times a board can be folded in two directions without breaking, under conditions specified in Standard D2176-69.
• Stiffness is defined as flexural rigidity and is determined by the bending moment in g-cm.
• Linerboard as used herein, is a medium-weight paper product used as the facing material in corrugated carton construction. Kraft linerboard is linerboard made according to the kraft process, and is well known in the industry. Folding carton board is a medium to heavy weight paper product made of unbleached and/or bleached pulps of basis weights from 40-350 g/m2.
• the invention comprises steps of 1) heating a board produced from either unbleached or bleached kraft pulp to an internal temperature of at least 400°F (205°C) for a period of time sufficient to increase the wet strength of the board; and 2) rewetting the board immediately after the heat treatment to at least 1% moisture by weight. These steps are followed by conventional drying and/or conditioning of the treated board. It is to be understood that steps 1 and 2 can be repeated several times.
• starch is added prior to heating. Every year, the paper industry comsumes millions of pounds of starch -- an inexpensive natural polymer closely related to cellulose in chemical composition. Preparations of starch are added to papers and board compositions principally to improve their dry strength and their surface properties (J.P. Casey, Pulp and Paper, 3rd edition, pp. 1475-1500, 1688-1969, 1981).
• the invention comprises steps of 1) adding starch preparation into the pulp slurry or onto surface of formed paper or board; 2) heating the said paper or board to an internal temperature of at least 400°F (205°C) for a period of time sufficient to increase the wet strength of the product; and 3) rewetting the product immediately after the heat treatment to at least 1% moisture by weight. These steps are followed by conventional drying and/or conditioning of the treated product. It should be understood that steps 1 and 2 or 1,2, and 3 can be repeated several times.
• Our treatment principally differs from conditioning in that we add water, by spraying or otherwise, to a very hot and dry paper or board at the very end of the heat treatment, without intermediate cooling. It is critical to our process that water be applied to the product while it is still hot, certainly above 50°C (122°F), and preferably above 205°C (400°F). Another heat treatment or drying step may follow rewetting, on or off the machine, during a subsequent operation such as sizing, coating or calendering.
• the invention can be carried out either on a conventional papermaking machine or off the machine in an oven after a size-press.
• a starch solution is added either to the paper pulp, prior to forming, or to a formed product in any of various ways known in the art.
• the invention is preferably practiced on a papermaking machine.
• the water content of the web must first be reduced to at least 40% by weight and preferably to within the 10-15% range.
• Sufficient heat is then applied to the board to achieve an internal paper temperature of at least 400°F (205°C).
• the heat can be applied in the form of hot air, superheated steam, heated drying cylinders, infrared heaters, or by other means.
• the invention may be practiced by heating paper product in an oven after a size-press.
• the internal temperature of the board should be brought to at least 400°F for at least 10 sec. Again, the nature of the heat source is not important.
• water is applied to it, preferably by spraying. Even though one effect of the water application is to cool the paper, it is important that the paper not be allowed to cool substantially before the water application.
• the heat treated and rewetted paper is then cooled, conditioned, and calendered according to conventional proce­dure.
• the invention has been practiced as described in the following examples. The improvement in board quality will be apparent from an examination of the test results listed in the tables below.
• a bleached kraft board with ambient moisture content of 5.0% (no HT) was tested for various properties of interest in both the machine direction (MD) and the cross-machine direction (CD).
• a portion of the board was then heat treated at 410°F (210°C) for 15 seconds (HT).
• a portion of the heat-treated board was immediately rewetted to 10.6% moisture content and then dried conventionally (HT & RW). Both samples were conditioned for 48 hours at 70°F (21°C), 65% relative humidity and were then tested. Properties of these samples are given in Table I. It can be seen that heat treating alone produces a substantial increase in stiffness, but some reduction in folding endurance. The latter property is restored, and more, by rewetting, which causes only a slight decrease in stiffness. The net result is a significant improvement in both properties.
• a commercial bleached kraft board (C) was wetted to contain 10.5% moisture by weight and heat treated at 410°F (210°C) for 26.5 seconds (HT). The board was conditioned for 48 hours under standard (70°F, 65% relative moisture) conditions. Resultant board properties are listed in Table II
• a bleached kraft board identical to that used for Example 1 was wetted to 10.2% moisture content and heat treated at 406°F (208°C) for 9 seconds (HT).
• a portion of the heat-treated board was immediately rewetted to 1.5% moisture content and then heat treated under same conditions again for 9 seconds (HT & RW). Both samples were conditioned for 24 hrs. under standard conditions and were the tested. Properties of these samples are given in Table III.
• the bleached kraft board in Example 2 was sized with corn starch (pick-up was 2.8 lb/3000 ft2). One portion of the sized board was conventionally dried (110°C for 9 seconds [C]). A second portion was heat treated at 410°F (210°C) for 28.8 seconds, without intermediate drying (HT). A third portion of the sized board was heat treated for 14.3 seconds under identical conditions, rewetted to contain 15% moisture by weight and heat treated again for 14.3 seconds (HT & RW). The board was conditioned for 48 hours under standard conditions. Resultant board properties are listed in Table VI. Notably conventional drying did not improve the wet tensile of the sized board vs. the unsized one; however, both the wet tensile and stiffness of the heat-treated sized board is higher than that of the unsized board.
• a mill sized bleached kraft board sample (C) was wetted to 10.9% moisture content and then treated at 410°F (210°C) for 15 seconds (HT). A portion of heat-treated board was rewetted and dried conventionally (HT & RW). All the samples were conditioned for 48 hours under standard conditions. Properties of these samples are given in Table VII.
• a sample never dried kraft linerboard grade pulp having a kappa number at 110 and Canadian Standard Freeness of 750 was slurried in water and starch preparation was added to the slurry in the amount of 1% of the oven dried pulp weight.
• the starches were "cooked" in water according to conventional practice to contain 8% of starch by weight.
• a dispersion of the pulp fibers was converted to handsheets using 12x12 inch square sheet mold. The quantity of the fibers in the dispersion was adjusted to give a sheet weight of 19 grams in the oven dry state, said weight being close to that of an air dried; 42 lb/1000 ft2 commercial linerboard sheet. The sheets were pressed at 60 psi prior to further treatments.
• a control sample (C) of handsheets was dried in a conventional dryer (Emerson speed dryer, model 10) at 230°F (110°C). The rest of the samples was heat treated at 428°F (220°C) for 15 seconds (HT). All the samples were conditioned for 48 hours under standard conditions. Resultant properties are listed in Table IX. One can see that wet tensile of samples containing starch is higher that that of both control and heat treated samples not containing starch.

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Citations (2)

• 1986
  • 1986-08-20 DE DE8686111512T patent/DE3680047D1/de not_active Expired - Lifetime
  • 1986-08-20 EP EP86111512A patent/EP0213545B1/de not_active Expired - Lifetime
  • 1986-08-22 KR KR1019860006957A patent/KR870002331A/ko not_active Withdrawn
  • 1986-08-22 FI FI863421A patent/FI85399C/fi not_active IP Right Cessation
  • 1986-08-22 BR BR8604010A patent/BR8604010A/pt unknown

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