JPS6285096A - Heat treatment of paper product and starch added paper product - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to papermaking technology, and relates to the field of papermaking, in which a paper product formed in rough form is treated with heat and then rewetted.
It relates to improving paper quality such as dry and wet stiffness, wet tensile strength, and opacity.

[Prior Art] In papermaking technology, it is customary to wet-press felt fields of fibers and dry them on heated rolls.

There is currently considerable interest in improving various properties of paper and board.

The tensile properties that can be quantified for paper include, in particular, wet and dry tensile strength, folding strength, stiffness, compressive strength, and opacity. Which properties are desirable to improve depend on the intended use of the paper product. For example, in the case of milk carton boards, stiffness is of paramount importance. Linerboard has three properties of particular interest: wet strength;
It has high bending strength and high humidity compressive strength.

All of these properties can be measured by known standard tests. As used herein, "wet strength" is defined by the American Society for Testing End Materials (AST).
M) means wet tensile strength measured according to standard D 829-48. 'Bending strength' means AST
It is defined as the number of times a board can be bent in two directions without breaking under the conditions specified in M D 2176-69.

``Stiffness'' is defined as bending stiffness and is determined by bending moment); -cm. ° used here
``Linerboard is a medium weight paper product used as a facing in corrugated carton construction. Kraft linerboard is linerboard manufactured by the kraft process and is well known in the industry.

Folded carton board is a medium to heavy weight paper product made from unbleached and/or bleached bulbs with a basis weight of 40 to 350 g/m2.

Previous workers in this field have recognized that high temperature treatment of linerboard can improve its wet strength. For example, E.

Back)'s Wet Stiffness Pie Heat
Treatment of the Running Web, Valve End Vapor Canada, Volume 77, No. 12,
No. 97-106 (December 1976) ("Wetst
ifness by heat treatment
of the runningweb'', Pu1p
& Paper (: anada, vol, 77, No.
, 12. pp, 97-106 (Dec, 1976)
) Please refer to This improvement, or increase, is due to the development and cross-linking of naturally occurring lignins and other polymers, a phenomenon that occurs even when no conventional synthetic resins or other binders are used.
It may be sufficient to retain the wet strength of the product.

It was previously thought that improvements in wet strength through heat curing were only achieved at the expense of increased brittleness (ie, decreased folding strength). A brittle or brittle board is unacceptable for many applications that involve subsequent deformation. Therefore, heat treatment alone to develop the wet strength of vaporboard and cartonboard has not been widely accepted. As Dr. Buck pointed out in the above article, "heating conditions must be selected to balance the desired wet stiffness increase with concomitant weakening in dry climates." Also, U.S. Pat.
, 875, 680, Dr. Buck discloses a method of heat treating ready-made corrugated boards to fix previously introduced resin, the purpose of which is to pass the embrittled material through a corrugator. The goal is to prevent people from doing so.

It is clear that improvements in stiffness and wet strength were previously thought to be incompatible with improvements in folding strength.

It is therefore an object of the present invention to produce a linerboard with both improved stiffness and wet strength, as well as improved folding strength.

To this end, a heat treatment method has been developed which allows not only to increase the stiffness and wet strength of different lid boards, but also to laterally and unexpectedly preserve the folding strength of these boards. Broadly speaking, the invention consists of the following processing steps.

That is, (1) boards made from either unbleached or bleached kraft valves must be heated to at least 205°C (40°C).
(2) heating the board to a moisture content of at least 1% by weight and then immediately reheating the board to an internal temperature of This is a moistening process. Following these steps, the treated board is subjected to conventional drying and/or drying.
Or subjected to moisture adjustment. Said steps (1) and (2)
) may be repeated several times.

The present invention produces a product that has a folding strength that is significantly superior to that of similar boards that have increased stiffness and wet strength through heat treatment alone. This means that
This is clearly demonstrated by the test examples below.

According to one embodiment of the invention, starch is added before heat treatment. Each year, the paper industry consumes millions of pounds of starch, an inexpensive natural polymer that is similar in chemical composition to cellulose.

Starch preparations are added to paper and board compositions primarily to improve their dry strength and surface properties (J. P. Kasei, Valve End Vapor, 3rd edition, 1475-15.
00 pages, 1688-1969, 1981,
J.

P, Ca5ey, Pu1p and Pa
per, 3rd editionPP, 1475
~1500. 1688-1969. 1981)
.

We have found that heat treatment surprisingly improves the wet strength of starch-containing papers and boards.

Broadly speaking, the present invention consists of the following processing steps. (1) adding a starch formulation into the valve slurry or onto the surface of the formed paper or board; (2) adding the starch formulation to the surface of the formed paper or board;
heating to an internal temperature of 400° F. for a period of time sufficient to increase the wet strength of the product;
3) The board is heated to a moisture content of at least 1% by weight and then immediately rewetted.

Following these steps, the product is subjected to conventional drying and/or moisture conditioning. Said steps (1) and (
It is to be understood that 2) or (1), (2) and (3) may be repeated several times.

The process produces products with folding strength that is significantly superior to that of similar products whose stiffness and wet strength have been increased by heat treatment alone or by the addition of starch alone. This is clearly demonstrated by the test examples described below.

Of course, those skilled in the art will recognize the need to condition the product to normal moisture content after the very high temperature treatment. For example, U.S. Patent 3,395,219
Please refer to A certain degree of re-7? Moisturizing is usually done, but the properties of the product are not even tested before the moisture adjustment. However, conventional rehumidification occurs after the product has been substantially cooled.

The process of the present invention differs primarily from moisture conditioning in that water is added to the very hot dry vapor or board by spraying or other means only at the end of the heat treatment, rather than immediately cooling it. That's true. the product while it is still hot, e.g.
℃ (122°F) or higher, preferably 205°C (400°C
°F), it is essential to add water. Other heat treatment or drying steps may be performed after rewetting, mechanically or non-mechanically, during subsequent operations such as sizing, coating or calendering.

According to the invention, the internal temperature of the board is at least 232°C.
(450°F) because it provides greater stiffness and wet strength. The reason is that the higher the temperature, the less time is required to hold the steps necessary to promote bonding, and therefore the less time there is for fiber degradation to occur. Also,
Shorter holding times allow higher production rates.

Although the invention can be practiced over a range of temperatures, pressures and hold times, these factors are interrelated. For example, the higher the temperature used, the shorter the holding time of the heat treatment step, and vice versa.

For example, 289°C (550°C) is required to achieve the desired improvement.
In case of F), it was found that 2 seconds is sufficient for the holding time; on the other hand, in case of 216″I: (420″F)″, a considerably longer holding time is required.

Preferred Embodiments of the Invention The invention can be carried out in an oven after the sizing press with or without conventional papermaking machinery. To add starch as a first step when practicing the present invention, add starch to either the paper bulb in the forming chamber or to the product formed by any of a variety of methods known in the art. Add water solution.

Rather, the invention can be implemented on a paper machine. The water content of the web should initially be at least 40%, preferably between 10% and 10%.
The weight must be reduced within 15%. Sufficient heat is then applied to the board to reach an internal paper temperature of at least 205°C (400” F). This heat may be provided by hot air, superheated steam, heated drying cylinders, infrared heaters, or other sources. It can be added by any means.

Alternatively, the invention may be carried out by placing the paper product in a sizing press and then heating it in an oven. The internal temperature of the board is at least 205°C (40°C)
0" F) for at least 10 seconds. However, the nature of the heat source is not critical.

Following the heat treatment step, water is added, preferably by spraying, while the paper is still hot. Even though one effect of adding water is to cool the paper, it is important not to allow the paper to substantially cool before adding water.

The heat treated and rewetted paper is then cooled, moisture conditioned and calendered according to conventional procedures.

The invention was carried out as described in the Examples below. The improved board quality is evident upon inspection of the test results listed in the table below.

Example 5% ambient moisture content
) with Z blank craft) board (no HT:)
tested various properties of interest in both machine direction (MD) and cross-machine direction (CD) directions.

A portion of the board was heat treated (HT) at 210° C. (410” F.) for 15 seconds. The portion of the heat treated board was immediately rewetted to a moisture content of 10.8% and then Both samples, dried as (HT&RW)6, were moisture conditioned to 65% relative humidity at 21°C (70″F) and then tested.The properties of these samples are listed in Table 1. .

1st table tsubo ff1153.4 154.0 1544 (nb
/3000ft2) Calibus (thickness) 15.7 15°8 15.0 (mil) Modified tipper rigidity 121/60 131/
72 127/71MD/(:D (g-cm
) % rigidity improvement 8.3/2Q
,0 5.0/18.3MD/C:D MIT bending number 98/75 85/
70 131155MD/CD Note) MIT bending number: Folding strength test developed at the Massachusetts Institute of Technology Heat treatment alone causes a substantial increase in stiffness (a), but a slight decrease in folding strength. I understand that. The latter properties were restored, with only a slight decrease in stiffness caused by rough rewetting. The net result is a significant improvement in both properties.

Example 2 Commercially available bleached kraftboard (C) was moistened to 1°C, 5% by weight moisture and heated to 210'C (410"F).
) Heat treated for 26.5 seconds (HT). The boat was heated under standard conditions (21t (70°F, 165% relative moisture) for 4 hours.
Moisture was adjusted for 8 hours. The properties of the obtained board are shown in Section 1I.
List in the table.

Bleached kraft port identical to that used in Example 1 was moistened to a moisture content of 10.2% and heated at 209°C (406°C).
°F) for 9 seconds (HT). A portion of the heat treated board was immediately rewetted to a moisture content of 1.5% and then heat treated again for 9 seconds under the same conditions (HT&R
W). Both samples were hydrated for 24 hours under standard conditions before testing. The properties of these samples are listed in Table 2.

Tsubotsu weight 153゜4 154.5 155.3 (
flb/3000ft2) Calibus (J5 only) 15.7 18
．． 6 16.1 (mil) Modified tipper stiffness 121/60 132/
60 133/67M0/(:D (g-cm
) % stiffness improvement 9.110
! 1.9/11.7MD/CD Dry tensile strength 66.1/37.4 72
．． 9/38゜1 64.2/48.5MO/CD
(ub/in) Wet tensile strength 2.5/L, 8 5.
7/3.6 5.0/3.7MD/CD
(J2b/i port) % wet/dry tensile 6.6/4.4 14.
9/9.4 10.3/7, 5MO/(:D Crack resistance% 100/100 85/
7 94158 No-Crack MD/CD Immediate rewetting following the heat treatment step doubled the wet strength and improved the stiffness of the vaporboard, although other properties were slightly degraded. Two rewetting cycles were necessary to prevent severe brittleness caused by heat treatment alone.

Example 4 Samples of linerboard with 5.5% ambient moisture (noHT) were tested for various properties of interest.

A portion of the board was heat treated at 240° C. (464° F.) for 30 seconds and tested after moisture conditioning for 24 hours under standard conditions (HT).

The properties of the sample in machine direction only are listed in Table 1v.

Engineering optical control sample Heat treatment condition (no HT) (HT) Basis weight 4
2.5 41.4 (ub/3000ft”) Calibus (thickness) 12.5 12.
3 (mil) L&N rigidity 5150 (g-cm) STFI compression strong compression 40.9 48
．． 7 (Ilb/in) Wet tensile strength 5.9 28.4 (
ub/in) Bending strength 834 463 Number of times until failure Note) 5TFI compressive strength: This is a compression test developed by 5TFI, and is rated by the Swedish Forest Products Association (SVEN).
SKA TRASOR5KNING SINSTITUT
Refers to the test developed in E).

Example 5 - Other samples from the same liner boat were wetted to 8.5% moisture content and tested for various properties of interest (noHT)
.

A portion of the board was heat treated (HT) at 240°C (464°F) for 10 seconds. A portion of the heat treated board was immediately rewetted to a moisture content of 7.6% and dried as usual (HT&RW). Both samples were tested under standard conditions and hydrated for 24 hours. Machine direction only properties of these samples are listed in Table V.

Human control sample Heat treatment Heat treatment and rewetting properties (008) (HT) (HTst RW)
Basis weight 43.1 43.0 42.8 (
J2b/3000ft2) Calibus (thickness) 12.7 13.1
12.8 (mil) L&N stiffness 53 62
58 (g-cm) STFI compression strong compression 41.0
48.3 47.8 (nb/in) Wet tensile strength 5.7 19.
9 24.3 (ub7in) Bending strength 854 449
Heat treatment and rewetting for 751 times until failure significantly improved the strength and stiffness properties, although only the folding strength decreased slightly. In all of the above examples, our post-treatment bending strength was at least 85% of that of the initial board.

Example 6 Sized with pure white kraft board cornstarch (in Example 2) (pickup = 2.8u b/3)
000 ft”). A portion of the sized board was conventionally dried (110° C. for 9 seconds [C]).

The second part was heated to 210°C (41°C) without intermediate drying.
(0°F) for 28.8 seconds (HT). 14.3 The third part of the sized board in the same condition
It was heat treated for seconds, re-wetted to contain 15% by weight of moisture, and heat treated again for 14.3 seconds (HT&RW). The board was conditioned for 48 hours under standard conditions. The properties of the obtained board are listed in Table 71. Conventional drying did not significantly improve the wet tensile of sized boards relative to unsized boards. However, both the wet tensile and stiffness properties of the sized and heat treated board are higher than those of the unsized board.

Example 7 A mill sized white kraftboard sample (C) was wetted to a moisture content of 10.9% and then heat treated at 210°C (410°F) for 10 seconds (HT). . A portion of the heat treated board was rewetted and dried as usual (HT&RW). All samples were rehydrated for 48 hours under standard conditions.

The properties of these samples are listed in Table 2.

5 ■Person weight 153.4 154.5 155.3 (
, i2b/30QOft2) Calibus (thickness) 15.7 16.
6 16.1 (mil) Modified stiffness 121/60 132/
60 133/67 Rigidity improvement%
9.110 9.9/11.7
Dry bow 1 bow length MD/CD 66.1/3
7.4 72.9/38.1 6
4.2/48 5 Wet Tensile MD/CD 2.5
/L, S 5.7/3.6 5.0/3
．． 7" strength retention, 6.6/4.4
14.9/9.4 10.3/7.5% (MD
/C1)) Crack resistance% 100/100 85/
7 94158 Uncracked MD/CD Example 8 Three unbleached kraft linerboard samples (C) were sized with different amounts of starch and then 208
Heat treated (HT) at 406° F. for 30 seconds.

All samples were rehydrated for 48 hours under standard conditions. Properties of the obtained linerboard are listed in Table 1.

Table 1 n b/1000ft2 Caliper (thickness) 13.1 13.4
13.7 13.8 13.6 (mil) Tipper stiffness 92.5 100.5 9
1,4 94.5 94.5 (g-cm) Dry tensile f! , b/in 105.3 87.
7 89.9 93.9 97.7 Wet bow IJ length ub/in 7.9 13
．． 8 14.6 [,81L2 wet strength retention 1% 7.5 15.7 15.5
17.9 18.6MIT bending
1702 ' 2064 1389 14
:15 1740 Example 9 A sample of completely undried kraft liner board grade valve having a Kappa number of 110 and a Canadian Standard freeness of 750 was suspended in water and suspended in 1% by weight of oven dried foot starch preparation. added to the liquid. The starch was made by conventional methods to contain 8% starch by weight in water. The dispersion of bulb fibers was converted into hand sheets using a 12 x 12 square inch sheet forming machine. The amount of fiber in the dispersion was adjusted to give an oven-dried sheet weight of 19 g. The above weight is the air dry weight (commercially available linerboard sheets are 4 lb/1000 ft2).
).

The sheet was pressed at 60 psi before further processing.

The handsheet control sample (C) was dried in a conventional dryer (Emerson Speed Dryer, Model 10) at 110°C (
The remainder of the sample was dried at 220" F.).
Heat treated for 15 seconds at 428”F (HT
). All samples were rehydrated for 48 hours under standard conditions. The obtained properties are listed in Table 2. What is the wet tensile strength of the sample with starch for both the control and heat-treated samples without starch? It can be seen that Wτ is higher than the leap length.

Claims (1)

[Claims] 1. A method for improving the stiffness, wet strength and opacity of a kraft paper product while maintaining its acceptable flexibility, comprising: The method characterized in that the product is heat treated and the product is immediately rewetted in the next heat treatment step before the product has substantially cooled. 2. A method according to claim 1, characterized by incorporating a starch preparation into the paper product. 3. Before the heat treatment step, the product contains 1.0-40% by weight
3. A method according to claim 1, characterized in that the initial water content is in the range of . 4. A method according to claim 1 or 2, characterized in that during the rewetting step, the product is rewetted to a moisture content in the range from 1.0 to 20% by weight. 5. The amount of starch preparation added is 0.2~
Claim 2 in the range of 10% by weight
The method described in section. 6. The method of claim 1, wherein the paper product is milk carton board. 7. The heat treatment temperature is 140-250°C (284-48°C
3. A method as claimed in claim 1 or claim 2, characterized in that the temperature is maintained at a temperature of 2 DEG F. for a period of time ranging from 0.5 to 120 seconds. 8. During the heat treatment step, the pressure on the paper product is
3. A method according to claim 2, where the pressure is equal to or less than normal papermaking pressures. 9. The method according to claim 1 or 2, wherein the paper is a folding carton board. 10. The method according to claim 1 or 2, when the paper is linerboard. 11. The liner board weighs about 205g/m^2 (42
11. The method according to claim 10, wherein the method has a basis weight of lb/1000ft^2). 12. The folding carton board weighs about 260g/m
The method according to claim 9, wherein the material has a basis weight of 160 lb/3000 ft^2. 13. A folding carton board with high rigidity and high folding strength produced by the method according to any one of claims 1 to 12. 14. A linerboard with high wet strength and high folding strength produced by the method according to any one of claims 1 to 12. 15, at least 2.63 KN/m (15 lb/in)
Linerboard according to claim 14, having a wet strength of at least 85% of the folding strength of the board before being subjected to both heat treatment and rewetting stages.