EP0213545A1 - Method of producing a Kraft paper product - Google Patents
Method of producing a Kraft paper product Download PDFInfo
- Publication number
- EP0213545A1 EP0213545A1 EP86111512A EP86111512A EP0213545A1 EP 0213545 A1 EP0213545 A1 EP 0213545A1 EP 86111512 A EP86111512 A EP 86111512A EP 86111512 A EP86111512 A EP 86111512A EP 0213545 A1 EP0213545 A1 EP 0213545A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- product
- paper
- board
- linerboard
- range
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
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
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- 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
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- 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
Abstract
Description
- 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.
- In the art of papermaking, it is customary to subject felted fibers to wet pressing and then to drying on heated rolls.
- There is currently considerable interest in improving various properties of paper and boards. 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.
- All of these properties can be measured by well-known standard tests. As used herein, then, "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.
- Prior workers in this field have recognized that high-temperature treatment of linerboard can improve its wet strength. See, for example E. Back, "Wet stiffness by heat treatment of the running web", Pulp & Paper Canada, vol. 77, No. 12, pp. 97-106 (Dec. 1976). This increase has been attributed to the development and cross-linking of naturally occurring lignins and other polymers, which phenomenon may be sufficient to preserve product wet strength even where conventional synthetic resins or other binders are entirely omitted.
- It is noteworthy that wet strength improvement by heat curing has previously been thought attainable only at the price of increased brittleness (i.e., reduced folding endurance). Embrittled board is not acceptable for many applications involving subsequent deformation, and therefore heat treatment alone, to develop the wet strength of linerboard and carton board, has not gained widespread acceptance. As Dr. Back has pointed out in the article cited above, "the heat treatment conditions must be selected to balance the desirable increase in wet stiffness against the simultaneous embrittlement in dry climates." Also, in U.S. Patent 3,875,680, Dr. Back has disclosed a process for heat treating already manufactured corrugated board to set previously placed resins, wherein the specific purpose is to avoid running embrittled material through a corrugator.
- It is plain that improved stiffness and wet strength, on one hand, and improved folding endurance, on the other, were previously thought to be incompatible results.
- It is, therefore, an object of the invention to produce linerboard having both improved stiffness, and wet strength, and improved folding endurance.
- With a view to the foregoing, a heat treatment process has been developed which dramatically and unexpectedly increases not only the stiffness and wet strength of different boards, but also preserves their folding endurance. In its broadest sense, 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.
- This method produces a product having folding endurance greatly exceeding that of similar board whose stiffness and wet strength have been increased by heat alone. This is clearly shown by our tests exemplified below.
- According to one embodiment of the invention, 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).
- We have found that heat treatment unexpectedly improves the wet strength of papers and boards containing starch. In its broadest sense, 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.
- This method produces a product having folding endurance greatly exceeding that of similar product whose stiffness and wet strength have been increased by heat alone, or by starch addition alone. This is clearly shown by our tests exemplified below.
- Of course, those skilled in the art will recognize the necessity of the product conditioning to a normal moisture content after this very hot treatment. See, for example, U.S. Patent 3,395,219. A certain amount of rewetting is normally done, and in fact product properties are never even tested prior to conditioning. However, conventional rehumidification is done after the product has substantially cooled.
- 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.
- We prefer to raise the internal temperature of the board to at least 450°F (232°C) during the heat treating step, as greater stiffness and wet strength are then achieved. This may be because at higher temperatures, shorter step duration is necessary to develop bonding, and there is consequently less time for fiber degradation to occur. Also, shorter durations enable one to achieve higher production speeds.
- While the invention may be practiced over a range of temperatures, pressures and duration, these factors are interrelated. For example, the use of higher temperatures requires a heat treating step of shorter duration, and vice-versa. For example, at 550°F (289°C), a duration of 2 seconds has been found sufficient to obtain the desired improvements, while at 420°F, considerably longer is required.
- The invention can be carried out either on a conventional papermaking machine or off the machine in an oven after a size-press. When starch is added, as a first step in carrying out the invention, 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.
- Alternatively, 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.
- Following the heat treating step, and while the paper is still hot, 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.
-
- 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.
- A sample of a linerboard with ambient moisture at 5.5% (no HT) was tested for various properties of interest. A portion of the board was then heat treated at 464°F (240°C) for 30 seconds and tested after conditioning for 24 hours under standard conditions (HT). Properties of the sample in the machine direction only are given in Table IV
- Another sample of same linerboard as in was wetted to 8.5% moisture content and then tested for various properties of interest (no HT). A portion of the board was then heat treated at 464°F (240°C) for 10 seconds (HT). A portion of the heat-treated board was immediately rewetted to 7.6% moisture content (HT & RW) and then dried conventionally. Both samples were conditioned for 24 hours under standard conditions and tested. Properties of these samples in the machine direction only are given in Table V.
- 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.
Claims (15)
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US76878485A | 1985-08-23 | 1985-08-23 | |
US76864385A | 1985-08-23 | 1985-08-23 | |
US768784 | 1985-08-23 | ||
US768643 | 1985-08-23 |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0213545A1 true EP0213545A1 (en) | 1987-03-11 |
EP0213545B1 EP0213545B1 (en) | 1991-07-03 |
Family
ID=27118074
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP86111512A Expired - Lifetime EP0213545B1 (en) | 1985-08-23 | 1986-08-20 | Method of producing a kraft paper product |
Country Status (5)
Country | Link |
---|---|
EP (1) | EP0213545B1 (en) |
KR (1) | KR870002331A (en) |
BR (1) | BR8604010A (en) |
DE (1) | DE3680047D1 (en) |
FI (1) | FI85399C (en) |
Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE650865C (en) * | 1933-06-08 | 1937-10-02 | Buckau R Wolf Akt Ges Maschf | Process for dewatering and drying raw material webs or sheets, such as cellulose, wood pulp or the like. |
US3875680A (en) * | 1972-04-18 | 1975-04-08 | Svenska Traeforskningsinst | Apparatus for producing wet stiff corrugated board |
-
1986
- 1986-08-20 DE DE8686111512T patent/DE3680047D1/en not_active Expired - Lifetime
- 1986-08-20 EP EP86111512A patent/EP0213545B1/en not_active Expired - Lifetime
- 1986-08-22 FI FI863421A patent/FI85399C/en not_active IP Right Cessation
- 1986-08-22 KR KR1019860006957A patent/KR870002331A/en not_active Application Discontinuation
- 1986-08-22 BR BR8604010A patent/BR8604010A/en unknown
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE650865C (en) * | 1933-06-08 | 1937-10-02 | Buckau R Wolf Akt Ges Maschf | Process for dewatering and drying raw material webs or sheets, such as cellulose, wood pulp or the like. |
US3875680A (en) * | 1972-04-18 | 1975-04-08 | Svenska Traeforskningsinst | Apparatus for producing wet stiff corrugated board |
Also Published As
Publication number | Publication date |
---|---|
FI85399B (en) | 1991-12-31 |
FI863421A (en) | 1987-02-24 |
FI863421A0 (en) | 1986-08-22 |
FI85399C (en) | 1992-04-10 |
EP0213545B1 (en) | 1991-07-03 |
BR8604010A (en) | 1987-06-30 |
DE3680047D1 (en) | 1991-08-08 |
KR870002331A (en) | 1987-03-30 |
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