CA1281567C - Heat treatment of paper products - Google Patents
Heat treatment of paper productsInfo
- Publication number
- CA1281567C CA1281567C CA000516414A CA516414A CA1281567C CA 1281567 C CA1281567 C CA 1281567C CA 000516414 A CA000516414 A CA 000516414A CA 516414 A CA516414 A CA 516414A CA 1281567 C CA1281567 C CA 1281567C
- Authority
- CA
- Canada
- Prior art keywords
- board
- paper
- linerboard
- folding endurance
- wet
- 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.)
- Expired
Links
Abstract
ABSTRACT
The stiffness, wet strength, opacity and folding endurance of paper products are improved by subjecting the products to steps of high temperature treatment and immediate rewetting.
The stiffness, wet strength, opacity and folding endurance of paper products are improved by subjecting the products to steps of high temperature treatment and immediate rewetting.
Description
. . 1;~81.567 ~S~ U.. QF TE~E~ INV13NTION
Field of the Invention:
This invention relates to the art of papermaking, particularly to treating of formed paper product witl, heat and subsequent rewetting to improve its properties, including dry and wet ~tiffness, wet tensile ~trength and opacity.
~_ In the art of papermaking, it i8 customary to subject felted fibers to wet pressing and then to drying on heated rolls.
There i8 currently considerable interest in improving varlous propertles of paper and boards. Quantifiable paper propertle~ lnclude: dry and wet tensile strength, folding endurance, stiffness, compressive strength, and opacity, among others. Which qualities ~hould desirably be enhanced depends upon the intended application of the product.
In the case o~ milk carton board, for example, stiffness i8 of utmost lmportance. Linerboard ha~ three qualities of particular lnterest, namely wet ~trength, folding endurance, and high humldity compression strength.
All of these properties can be measured by well-known ~tandard te~t~. A~ u~ed herein, then, "wet ~trength" means wet ten~lle strength as measured by American Society for Te~ting and Materials ~ASTM) Standard D829-48. "Folding endurance" is defined as the number of time~ a board can be ~olded in two directions without breaking, under conditions specified in Standard D2176-69. n 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 corr~gated - - - i . . 1~81567 !1 carton con~tructlon. Kraft llnerboard 1~ llnerboard made accordlng to the kraft p~ocess, and is well known ln the lndu~try. Foldlng carton board i~ a medlum to heavy weight paper product made of unbleached and/or bleached pulps of ba~is welghts from 40-350 g/m2.
Prior workers in this field have recognized that high-temperature treatment of linerboard can improve it~
wet ~trength, See, for example ~. Back, "Wet stiffne~s by heat treatment of the running web", Pulp & Pa~eL Canada, vol. 77, No. 12, pp. 97-106 (Dec. 1976). Thi~ lncrea~e has been attributed to the development and cross-linking of naturally occurring lignins and other polymers~ which phenomenon may be sufflcient to preserve product wet strength even where conventional synthetic resins or other binders are entlrely omltted.
It iB noteworthy thnt wet strength improvement by heat curing ha~ previously been thought attainable only at the prlce of lncreased brittleness ~i.e., reduced folding endurance). Embrittled board iB not acceptable for many appllcations involving subsequent deformation, and therefore heat treatment alone, to develop the wet strength of linerboard and aarton board, has not gained widespread acceptance.
As Dr. Back has polnted out in the article cited above, ~the heat treatment condition~ must be selected to balance the desirable lncrease in wet ~tiffness against the simultaneous embrittlement in dry climates." A1BO, in U.S. Patent 3,B75,680, Dr. Back has disclosed a proce~ for heat treating already manufactured corrugated board to set previously placed resins, wherein the specific purpo~e i~ to avoid running embrittled material through a corrugator.
~ 2 .. . 1~567 It iB plain that improv~d ~tifnes~ and wet strength, on one hand, and lmproved foldlng endurance, on the other, were previously thought to be $ncompatible results.
It is, therefore, an object of the invention to produce llnerboard having both improved stiffne~, and wet ~trength, and improved folding endurance. Another goal i~ to achieve that ob~ective without re~o~ting to synthetic resin~ or other added binders.
With a view to the foregoing, a heat treatment process has been developed which dramatlcally and unexpectedly lncreases not only the stiffness and wet strength of different boards, but also preserves their folding endurance. In its broadest ~ense, the inven~ion comprise~ steps of 1) heatlng a board produced from either unbleached or bleached kraft pulp to an internal temperature of at least 400F
~205C) for a period oE time sufficlent to increase the wet strength o the board~ and 2) rewetting the board immediately after the heat treatment to at lea6t 1% moisture by weight. These steps are followed by conventional drying and/or conditioning of the treated board. It is to be understood that ~teps 1 and 2 can be repeated ~ever~l times.
This method produces a product having folding endurance greatly exceeding that of similar board whose stiffness and wet strength have been increa6ed by heat alone. Thi~ 1~ 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 1'~81567 even tested prior to conditioning. ~lowever, conventional rehumidiflcation i~ done after the product has sub~tantially cooled.
Our treatment principally differs from conditioning in that we add water, by spraying or otherwi6e, 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 50C (122F~, and preferably above 205C ~400F). Another heat treatment or drying step may follow rewetting, on or off the machine, durlng a subsequent operation such as sizing, coating or calendering.
We prefer to raise the internal temperature of the board to at lea~t 450F ~232C) during the heat treating step, a~ greater stlffness and wet ~trength are then achieved.
This may be because at higher temperatures, shorter step duration i8 neaessar~ to develop bondlng, and there is consequQntly 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-ver~a. For example, at 550F (289C~, a duration of 2 seconds has been found sufficient to obtain the desired improvements, while at 420F, considerably longer is required.
1;~815~7 ~ "
The lnvention can be carrled out elther on a conventional papermaking machlne or off the machine in an oven after a slze-press.
The lnvention i5 preferably practiced on a papermaking mach$ne. The water content of the web must flrst be reduced to at least 404 by weight and preferably to within the 10-15~ range. Sufficient heat i8 then applied to the board to achieve an lnternal paper temperature of at lea~t 400~
~205C). The heat can be applled in the form of hot air, superheated steam, heated drying cyllnders, infrared heaters, or by other means.
Alternatively, the invention may be practiced by heatlng paper product in an oven after a size-press.
The lnternAl temperature of the board should be brought to at lea~t 400F for at lea~t 10 ~ec. Again, the nature of the hea~ ~ource 1B not important.
Followlng the heat treating step, and while the , papaer 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 proce-dure. The invention has been practiced as de~cribed in the following examples. The improvement in board quality will be apparent from an examination of the test results listed in the tables below.
. 5 ~,~8~S67 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 (M~) and the cross-machlne direction (CD). A portion of the boar~ wa8 then heat treated at 410F (210C) for 15 seconds (HT).
A portion of the heat-treated board wa6 immediately rewetted to 10.6% moi~ture content and then dried conventionally (HT & RW). Both samples were conditioned or 48 hour~ at 70F (21C), 65~ relative humidity and were then tested.
Propertles of these samples are given in Table I.
Co~trol ~eat Rewetted ~ampl~ T~ented Sample ELQ~L$Y ~no ~T2 (~T) lUI~R~) ~a~ iB weigh~
(lb/3000 ft ) 153.4 154.0 154.3 Caliper (mil~) 15.7 15.8 15.0 Corrected Taber stif-ness MD/CD ~g-cm) 121/60 131/72 127/71 ~ stiffnes6 lmprove-ment MD/CD -- 8.3/20.05.0/18.3 MIT Fold counts It can be seen that heat treating alone produces a substantial increa8e in stiffne3s, 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 i8 a significant improvement in both properties.
1~8~S67 I ~
A bleached kraft board identical to that used for Example 1 was wetted to 10.2~ moisture content and heat treated at 406F ~208C) for g ~econd~ (~lT). A ~ortion of the heat-treated board was immediately rewetted to 1.5~
molsture content and then heat treated under same conditions agaln for 9 s~conds ~HT 6 RW) . Both ~mple~ were c~nditloned for 24 hrs. under standard condition~ and were then tested.
Propertles of these samples are given in Table II.
Control Deat Rewetted Sample Treated Sample ~LQV~L~Y 1DQ~ T) (~T&RW) Basis weigh~
(lb/3000 ft ) 153.4 154.5 155.3 Callper ~mils) 15.7 16.6 16.1 Corrected Taber stiff-ness MD/CD ~g-cm~ 121/60 132~60 133/67 ~ stiffne~s lmprove-ment MD/CD '-- 9.1/0 9.9/11.7 Dry Tensile Strength MD/CD ~lb/in) 66.1/37.472.9/38.164.2/48.5 Wet Tensile strength MD/CD ~lb/ln) 2.5/1.6 5.7/3.6 5.0/3.7 ~ Wet/Dry Tensile MD/CD 6.6/4.4 14.9/9.4 10.3/7.S
Cracking resistance ~ not cracked MD/CD100~100 85/7 94/58 The steps of heat treating followed immediately by rewetting doubled wet strength and improved stiffness of the paperboard, with only a slight degradation of other properties. Rewetting was necessary to prevent the severe embrittling caused by heat treatment alone.
~ ~81.5G~ , ~P~3 A sa~ple of a llnerboard with ambient moi6tu~e at 5.5% (no ~T) was tested for various properties of interest.
A portlon of the board was then heat treated at 464F (240C) for 30 seconds and tested after conditioning for 24 hour~ under standard conditions (~T). Properties of the sample in the machine direction only are given in Table III.
~L~
Control ~eat Snmple Tre~ted ~ (IIT) :
Basls welgh~ j ~lb/3000 ft~) 42.5 41.4 Caliper (mils) 12.5 12.3 L & N Stiffness ~g-cm) . 51 50 STFI Compre~lon Strength ~lb~ln) 40.9 48.7 Wet Ten8ile Strength ~lb/in) 5.9 28.4 Folding Endurance cycles to failure 834 463 ~8~67 ~ ~l ~ ~ i Another ~ample of same linerboard wa~ wetted to 8.5~ moi~ture content and then tested for varlous properties of interest (no HT). A portion of the board was then heat treated at 464F (240C) for 10 seconds ~T). A portion of the heat-treated board was immediately rewetted to 7.6 moisture content (HT & RW) and then drled conventionally.
Both samples were conditioned for 24 hours under standard condltlons and tested. Properties o~ these sample~ in the machine direction only are given in Table IV.
~L~
Control neat ~T 6 ~ j 8nmple TreatedRewetted ~Q~r ~Q~ (IIT) ~L ' Bas iB weigh~
~lb/3000 ft ) 43.1 43.0 42.8 Caliper ~mils) 12.7 13.1 12.8 L h N Stiffne8 ~g-cm) '53 62 58 STFI Compre~sion Strength ~lb/in)41.0 48.3 47.8 Wet Tensile Strength ~lb/in) 5.7 19.9 24.3 Folding Endurance cycles to failure854 449 751 Heat treating and rewetting notably improved strength and stiffness properties with only a minor reduction in folding endurance. In all the above examples, folding endurance following our treatment was at lea~t 85~ that of the original boar . , 9 ;
815~i7 ~, Inasmuch as the invention is ~ubject to many variations and change~ in detail, the ioregoing description and example~ should be taken a~ merely illustrative of the lnvention defined by the following claims.
Field of the Invention:
This invention relates to the art of papermaking, particularly to treating of formed paper product witl, heat and subsequent rewetting to improve its properties, including dry and wet ~tiffness, wet tensile ~trength and opacity.
~_ In the art of papermaking, it i8 customary to subject felted fibers to wet pressing and then to drying on heated rolls.
There i8 currently considerable interest in improving varlous propertles of paper and boards. Quantifiable paper propertle~ lnclude: dry and wet tensile strength, folding endurance, stiffness, compressive strength, and opacity, among others. Which qualities ~hould desirably be enhanced depends upon the intended application of the product.
In the case o~ milk carton board, for example, stiffness i8 of utmost lmportance. Linerboard ha~ three qualities of particular lnterest, namely wet ~trength, folding endurance, and high humldity compression strength.
All of these properties can be measured by well-known ~tandard te~t~. A~ u~ed herein, then, "wet ~trength" means wet ten~lle strength as measured by American Society for Te~ting and Materials ~ASTM) Standard D829-48. "Folding endurance" is defined as the number of time~ a board can be ~olded in two directions without breaking, under conditions specified in Standard D2176-69. n 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 corr~gated - - - i . . 1~81567 !1 carton con~tructlon. Kraft llnerboard 1~ llnerboard made accordlng to the kraft p~ocess, and is well known ln the lndu~try. Foldlng carton board i~ a medlum to heavy weight paper product made of unbleached and/or bleached pulps of ba~is welghts from 40-350 g/m2.
Prior workers in this field have recognized that high-temperature treatment of linerboard can improve it~
wet ~trength, See, for example ~. Back, "Wet stiffne~s by heat treatment of the running web", Pulp & Pa~eL Canada, vol. 77, No. 12, pp. 97-106 (Dec. 1976). Thi~ lncrea~e has been attributed to the development and cross-linking of naturally occurring lignins and other polymers~ which phenomenon may be sufflcient to preserve product wet strength even where conventional synthetic resins or other binders are entlrely omltted.
It iB noteworthy thnt wet strength improvement by heat curing ha~ previously been thought attainable only at the prlce of lncreased brittleness ~i.e., reduced folding endurance). Embrittled board iB not acceptable for many appllcations involving subsequent deformation, and therefore heat treatment alone, to develop the wet strength of linerboard and aarton board, has not gained widespread acceptance.
As Dr. Back has polnted out in the article cited above, ~the heat treatment condition~ must be selected to balance the desirable lncrease in wet ~tiffness against the simultaneous embrittlement in dry climates." A1BO, in U.S. Patent 3,B75,680, Dr. Back has disclosed a proce~ for heat treating already manufactured corrugated board to set previously placed resins, wherein the specific purpo~e i~ to avoid running embrittled material through a corrugator.
~ 2 .. . 1~567 It iB plain that improv~d ~tifnes~ and wet strength, on one hand, and lmproved foldlng endurance, on the other, were previously thought to be $ncompatible results.
It is, therefore, an object of the invention to produce llnerboard having both improved stiffne~, and wet ~trength, and improved folding endurance. Another goal i~ to achieve that ob~ective without re~o~ting to synthetic resin~ or other added binders.
With a view to the foregoing, a heat treatment process has been developed which dramatlcally and unexpectedly lncreases not only the stiffness and wet strength of different boards, but also preserves their folding endurance. In its broadest ~ense, the inven~ion comprise~ steps of 1) heatlng a board produced from either unbleached or bleached kraft pulp to an internal temperature of at least 400F
~205C) for a period oE time sufficlent to increase the wet strength o the board~ and 2) rewetting the board immediately after the heat treatment to at lea6t 1% moisture by weight. These steps are followed by conventional drying and/or conditioning of the treated board. It is to be understood that ~teps 1 and 2 can be repeated ~ever~l times.
This method produces a product having folding endurance greatly exceeding that of similar board whose stiffness and wet strength have been increa6ed by heat alone. Thi~ 1~ 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 1'~81567 even tested prior to conditioning. ~lowever, conventional rehumidiflcation i~ done after the product has sub~tantially cooled.
Our treatment principally differs from conditioning in that we add water, by spraying or otherwi6e, 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 50C (122F~, and preferably above 205C ~400F). Another heat treatment or drying step may follow rewetting, on or off the machine, durlng a subsequent operation such as sizing, coating or calendering.
We prefer to raise the internal temperature of the board to at lea~t 450F ~232C) during the heat treating step, a~ greater stlffness and wet ~trength are then achieved.
This may be because at higher temperatures, shorter step duration i8 neaessar~ to develop bondlng, and there is consequQntly 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-ver~a. For example, at 550F (289C~, a duration of 2 seconds has been found sufficient to obtain the desired improvements, while at 420F, considerably longer is required.
1;~815~7 ~ "
The lnvention can be carrled out elther on a conventional papermaking machlne or off the machine in an oven after a slze-press.
The lnvention i5 preferably practiced on a papermaking mach$ne. The water content of the web must flrst be reduced to at least 404 by weight and preferably to within the 10-15~ range. Sufficient heat i8 then applied to the board to achieve an lnternal paper temperature of at lea~t 400~
~205C). The heat can be applled in the form of hot air, superheated steam, heated drying cyllnders, infrared heaters, or by other means.
Alternatively, the invention may be practiced by heatlng paper product in an oven after a size-press.
The lnternAl temperature of the board should be brought to at lea~t 400F for at lea~t 10 ~ec. Again, the nature of the hea~ ~ource 1B not important.
Followlng the heat treating step, and while the , papaer 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 proce-dure. The invention has been practiced as de~cribed in the following examples. The improvement in board quality will be apparent from an examination of the test results listed in the tables below.
. 5 ~,~8~S67 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 (M~) and the cross-machlne direction (CD). A portion of the boar~ wa8 then heat treated at 410F (210C) for 15 seconds (HT).
A portion of the heat-treated board wa6 immediately rewetted to 10.6% moi~ture content and then dried conventionally (HT & RW). Both samples were conditioned or 48 hour~ at 70F (21C), 65~ relative humidity and were then tested.
Propertles of these samples are given in Table I.
Co~trol ~eat Rewetted ~ampl~ T~ented Sample ELQ~L$Y ~no ~T2 (~T) lUI~R~) ~a~ iB weigh~
(lb/3000 ft ) 153.4 154.0 154.3 Caliper (mil~) 15.7 15.8 15.0 Corrected Taber stif-ness MD/CD ~g-cm) 121/60 131/72 127/71 ~ stiffnes6 lmprove-ment MD/CD -- 8.3/20.05.0/18.3 MIT Fold counts It can be seen that heat treating alone produces a substantial increa8e in stiffne3s, 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 i8 a significant improvement in both properties.
1~8~S67 I ~
A bleached kraft board identical to that used for Example 1 was wetted to 10.2~ moisture content and heat treated at 406F ~208C) for g ~econd~ (~lT). A ~ortion of the heat-treated board was immediately rewetted to 1.5~
molsture content and then heat treated under same conditions agaln for 9 s~conds ~HT 6 RW) . Both ~mple~ were c~nditloned for 24 hrs. under standard condition~ and were then tested.
Propertles of these samples are given in Table II.
Control Deat Rewetted Sample Treated Sample ~LQV~L~Y 1DQ~ T) (~T&RW) Basis weigh~
(lb/3000 ft ) 153.4 154.5 155.3 Callper ~mils) 15.7 16.6 16.1 Corrected Taber stiff-ness MD/CD ~g-cm~ 121/60 132~60 133/67 ~ stiffne~s lmprove-ment MD/CD '-- 9.1/0 9.9/11.7 Dry Tensile Strength MD/CD ~lb/in) 66.1/37.472.9/38.164.2/48.5 Wet Tensile strength MD/CD ~lb/ln) 2.5/1.6 5.7/3.6 5.0/3.7 ~ Wet/Dry Tensile MD/CD 6.6/4.4 14.9/9.4 10.3/7.S
Cracking resistance ~ not cracked MD/CD100~100 85/7 94/58 The steps of heat treating followed immediately by rewetting doubled wet strength and improved stiffness of the paperboard, with only a slight degradation of other properties. Rewetting was necessary to prevent the severe embrittling caused by heat treatment alone.
~ ~81.5G~ , ~P~3 A sa~ple of a llnerboard with ambient moi6tu~e at 5.5% (no ~T) was tested for various properties of interest.
A portlon of the board was then heat treated at 464F (240C) for 30 seconds and tested after conditioning for 24 hour~ under standard conditions (~T). Properties of the sample in the machine direction only are given in Table III.
~L~
Control ~eat Snmple Tre~ted ~ (IIT) :
Basls welgh~ j ~lb/3000 ft~) 42.5 41.4 Caliper (mils) 12.5 12.3 L & N Stiffness ~g-cm) . 51 50 STFI Compre~lon Strength ~lb~ln) 40.9 48.7 Wet Ten8ile Strength ~lb/in) 5.9 28.4 Folding Endurance cycles to failure 834 463 ~8~67 ~ ~l ~ ~ i Another ~ample of same linerboard wa~ wetted to 8.5~ moi~ture content and then tested for varlous properties of interest (no HT). A portion of the board was then heat treated at 464F (240C) for 10 seconds ~T). A portion of the heat-treated board was immediately rewetted to 7.6 moisture content (HT & RW) and then drled conventionally.
Both samples were conditioned for 24 hours under standard condltlons and tested. Properties o~ these sample~ in the machine direction only are given in Table IV.
~L~
Control neat ~T 6 ~ j 8nmple TreatedRewetted ~Q~r ~Q~ (IIT) ~L ' Bas iB weigh~
~lb/3000 ft ) 43.1 43.0 42.8 Caliper ~mils) 12.7 13.1 12.8 L h N Stiffne8 ~g-cm) '53 62 58 STFI Compre~sion Strength ~lb/in)41.0 48.3 47.8 Wet Tensile Strength ~lb/in) 5.7 19.9 24.3 Folding Endurance cycles to failure854 449 751 Heat treating and rewetting notably improved strength and stiffness properties with only a minor reduction in folding endurance. In all the above examples, folding endurance following our treatment was at lea~t 85~ that of the original boar . , 9 ;
815~i7 ~, Inasmuch as the invention is ~ubject to many variations and change~ in detail, the ioregoing description and example~ should be taken a~ merely illustrative of the lnvention defined by the following claims.
Claims (10)
1. A method of improving the stiffness, wet strength and opacity of a kraft paper product while maintaining acceptable flexibility thereof which consists of heating a paper product having an initial moisture content in the range of 1.0 to 40% by weight, at such a temperature that its internal temperature is at least 205°C and immediately following said heat treatment step, rewetting said paper product while said product is still at a temperature above 50°C to a moisture content in the range of 1.0 to 20% by weight.
2. The method according to claim 1 wherein said paper product is heated to a temperature of 289°C for 2 seconds.
3. The method of claim 1 wherein said paper product is milk carton board.
4. The method of claim 1 wherein said paper is folding carton board.
5. The method of claim 1 wherein said paper is a linerboard.
6. The method of claim 5 wherein said linerboard has a basis weight of about (42) lb/1000 ft2 (205 g/m2).
7. The method of claim 4 wherein said folding carton board has a basis weight of about 160 lb/3000 ft2 (260 g/m2).
8. A folding carton board of high stiffness and high folding endurance produced by the method according to claim 1.
9. A linerboard of high wet strength and high folding endurance produced by the method according to claim 1.
10. A linerboard as in claim 9, having a wet strength of at least 15 lb/in (2.63 KN/m) and a folding endurance of at least 85% of the folding endurance of the board prior to application of the heat treating and rewetting steps.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US76864385A | 1985-08-23 | 1985-08-23 | |
| US768,643 | 1985-08-23 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1281567C true CA1281567C (en) | 1991-03-19 |
Family
ID=25083082
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000516414A Expired CA1281567C (en) | 1985-08-23 | 1986-08-20 | Heat treatment of paper products |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS6285096A (en) |
| CA (1) | CA1281567C (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10206028B2 (en) | 2014-08-22 | 2019-02-12 | Pioneer Corporation | Damper and speaker apparatus |
-
1986
- 1986-08-20 CA CA000516414A patent/CA1281567C/en not_active Expired
- 1986-08-22 JP JP19796986A patent/JPS6285096A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| JPS6285096A (en) | 1987-04-18 |
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