US 3431162 A
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R. M. MORRIS Marh 4, 1969 CORRUGATD CONTAINERBOARD AND THE PROCES-S OF TREATING THE SAME Filed April e, 1965 l 1N VENTOR. RICHARD M. Monms Ammers United States Patent O 3 Claims ABSTRACT OF THE DISCLOSURE A water resistant linerboard which retains its strength under high humidity conditions is made by impregnating 1 to 5 lbs. per thousand square feet of a starch extended phenol-formaldehyde resin wherein the molecular weight ratio of formaldehyde to phenol ranges from 0.9 to 3.0 only into the outer surfaces of a rosin sized linerboard. The linerboard can be used to make corrugated containerboard in a conventional manner.
This invention relates to an article of manufacture and a process for making the same. More specifically, this invention relates to a corrugated containerboard treated by a unique process with resinous material to permit high performance of containers formed from the containerboard when they are exposed to high humidity or wet conditions.
In the manufacture of linerboard for use in the fabrication of corrugated containerboard, it is the practice to deposit pulp in a water carrier on a moving screen. The pulp is then pressed into a web and then dried. The linerboard is used to form corrugated containerboard by sandwiching a corrugated medium between a pair of spaced apart linerboards in a corrugating machine. The corrugated containerboard is then cut into blanks and scored to form containers for shipment of goods therein.
While the containers formed in the above-noted procedure have enjoyed a high degree of commercial success, this type of container is completely unsatisfactory when exposed to high humidity or wet conditions such as when shipping produce, dressed poultry, etc., or the like packed in ice. The exposure of the corrugated containerboard to the water and water vapors rapidly deteriorates the corrugated containerboard so that the board will completely collapse in a relatively short period of time. Accordingly, the industry has expended much time and effort to obviate this problem. One approach to the solution of this problem was to impregnate the linerboard and corrugated medium with a wax to form a water barrier and thereafter fabricate the corrugated containerboard. This approach has not been successful because the linerboard and corrugated medium cannot be satisfactorily fabricated into a containerboard on a conventional corrugating machine. Further, the wax impregnated linerboard and corrugated medium do not form barriers against the encroachment of water vapor into the containerboard; thus the containerboard would still rapidly deteriorate because of the presence of the water vapor. Another approach to the solution of this problem was to form the corrugated containerboard and then imprcgnate the same with a wax solution. However, this approach has not been successful because of the fact that the water vapors would still penetrate the wax coating on the corrugated containerboard and thus rapidly deteriorate the containerboard.
An object of this invention is to provide a linerboard for use in the fabrication of corrugated containerboard which is highly water resistant and will retain its strength properties under high humidity or wet conditions.
Another object of this invention is to provide a liner- ICC board impregnated with a wax and a thermosetting resin to form a water barrier within the linerboard.
Another object of this invention is to provide a linerboard which can be treated at the mill level and sub sequently used to form corrugated containerboard without additional equipment to treat the corrugated containerboard to make the same highly water resistant.
Another object of this invention is to provide a process for treating linerboard to make the same highly water resistant.
Another object of this invention is to provide a process for fabricating corrugated containerboard having high strength characteristics when exposed to high humidity or wet conditions by employing a combination of wax and thermosetting resin impregnated into the linerboard.
These and other objects and advantages will become manifestly clear to those skilled in the art when taken in conjunction with the detailed specification and drawings, wherein:
FIGURE l is a flow diagram schematically illustrating the process for treating the linerboard of the present invention.
FIGURE 2 is a cross sectional view of the linerboard taken on line 2 2 of FIGURE l.
FIGURE 3 is a cross sectional view of a corrugated containerboard formed in accordance with the present invention.
In the practice of the present invention, the linerboard is formed on a standard papermaking machine v1. The papermaking machine 1 is provided with a moving screen 2 extending around a pair of spaced apart rolls 3 and 4. Mounted along the upper run of the screen 2 is a plurality of upper press rolls 5 and a plurality of lower press rolls 6 for the purpose of removing excess water from the linerboard.
Mounted above the screen 2 at the end opposite the press rolls 5 and 6 is a primary column 7 containing rened pulp at a consistency of about 0.72% pulp and about 99.3% water. Mounted intermediate the primary column 7 and the pressure rolls 5 and 6 is a secondary column 8 containing refined pulp at about a 0.7% consistency and 99.3% water. The pH of the two stock solutions is controlled with aluminum sulfate, and/or sulfuric acid to a range of 4.0-6.0. The primary column and the secondary column are each provided with lines 9 and 10 for the purpose of depositing the pulp on the moving screen to form the lower web 11 from the primary column and an upper web 12 from the secondary column. The pulp in the primary column is provided with rosin at a rate of up to l0 lbs/ton for the purpose of sizing the paper or providing the paper with a reduced absorbency to water as is conventional in the art. Also, rosin is added to the pulp in the secondary column at a rate of up to l() lbs/ton along with from l to 5 lbs/ton of Paracol wax. Accordingly, as the webs 11 and 12 extend through the press rolls 5 and 6, the excess water is removed to provide a linerboard 28 having webs 11 and 12 adjacent each other with the upper web 12 being provided with from l to 5 lbs./ton of a Wax emulsion along with up to 10 lbs./ton of rosin in each layer 11 and 12.
From the papermaking machine 1, the web 28 is passed through a dryer 13 provided with a plurality of heated rolls 14 which remove the excess water and provides the linerboard with the requisite amount of moisture content.
As the web 28 leaves dryer 13, it passes around a guide roll 15 and into a sizing press 16. The sizing press 16 is provided with a pair of spaced apart rolls 17 and 18 mounted on approximately a parallel axis to properly size the web 28.
A thermosetting resin is impregnated into the outer surfaces of each of the webs 11 and 12 just prior to the web 28 entering the size press 16. This is brought about by placing a pool of thermoset resin 20 and 21 adjacent the rolls 18 and 17 respectively so that upon the entrance of the web 28 between the press rolls 17 and 18, the requisite amount of thermosetting resin will be irnpregnated into the surface thereof. Lines 22 and 23 are provided above the rolls 17 and 18 to ensure a requisite amount of thermoset resin in the pools 20 and 21. The amount of thermoset resin that is impregnated into each of the surfaces of the webs 11 and 12 may range from between l to lbs./M ft.2 of web, but preferably is between 2 and 3 lbs/M ft2 As the web 28 leaves the sizing press 16, it is conveyed around a guide roll 19 into a second dryer 24 provided with a plurality of heated rolls 25. The temperature of the dryer 24 may range from 300 F. to 450 F. with the web 28 being maintained within dryer 24 at from about 5 to 90 seconds. By regulating the time that the web 28 iS within dryer 24 and the temperature within the dryer 24, the thermoset resin that is impregnated into the surface of the upper and lower webs 12 and 11 is partially cured in addition to the moisture content being regulated to from 4% to 20% by weight to control the resin cure therein. As the web 28 leaves the dryer 24, it is formed into a roll 26 to be used in a conventional corrugating machine to form corrugated containerboard.
It has been found in practice that the amount of thermosetting resin added to each surface of the web 28 must be held to a level not in excess of that amount noted above to impart the desired level 0f rigidity to the web 28 since an amount over that limit will impart an embrittlement to the web 28 which will cause fracturing during subsequent converting operations into the shipping container itself. The thermosetting resin that may be employed with the process of the present invention may be any thermosetting resin having a low temperature cure such as phenol formaldehyde, urea formaldehyde, melamine formaldehyde, each having a molecular ratio to provide the low temperature and fast curing rate desired in this operation. It has been found that phenol formaldehyde resin having a molecular ratio of from .9 to 3 moles of formaldehyde to l mole of phenol provides satisfactory results in the practice of the present invention. If desired, an extender such as starch may be added to the thermosetting resin which functions not only as an extender, but as a buffer which prevents deep penetration of the thermosetting resin into the web 28. It should be noted that the thermosetting resin of phenol formaldehyde within the molecular ratio as noted above with the raw starch extender tends to hold the resin solids on the surface of the web 28 rather than penetrating deeply within the web 28. This is brought about by providing the total resin solids within a water vehicle up to total resin solids. Starch may be within the water vehicle up to about 10%. Accordingly, the phenolic resin solution may contain solids and 75% water to provide the requisite viscosity to impregnate the surface of the web 28.
After the linerboard has been rolled into roll 26, it may be used in the formation of corrugated containerboard in the conventional manner. This is carried out by employing a conventional corrugating medium having no additives except for from 3 to 10 lbs./ M ft?, preferably 6 to 7 lbs./M ft.2 of a modified paratiin-base Wax impregnated therein. Corrugated medium is extended through the corrugating machine and is adhered between a pair of webs 28 as indicated in FIGURE 3. As is conventional in the art, the corrugated medium is adhered to the surfaces of the web portions 11 by conventional adhesives and then fully set by passing the corrugated containerboard through a heating medium. This heating medium not only fully sets the glue adhering the corrugated medium 27 to the surfaces of portions 11, but also functions to fully cure the resins within the portions 11 and 12 that were impregnated therein by the sizing press 16.
In this manner, a corrugated containerboard having high water resistance can be made without further processing. The corrugated containerboard as shown in FIG- URE 3 need only be cut and scored in the usual manner and then fabricated into a shipping container. The amount of thermosetting resins within the linerboard 28 greatly increases the wet strength of the corrugated containerboard and prevents the deterioration of the strength of the shipping container formed therefrom due to the penetration of water vapors and liquid water into the linerboard and corrugating medium.
In order to illustrate the merits of the present invention, tests were conducted on a regular grade shipping container impregnated with a conventional wax and a container formed from the corrugated containerboard as herein defined. The results of these tests indicate that the compression strength of each one under certain prescribed conditions are as follows:
Regular Additive Run Test conditions grade treated (lbs.) (lbs.)
1 72 F. at 53% RH for 24 hrs 956 1,550 v 72 F at 00% RH for 24 hrs 473 784 3 hrs. water shower... 92 583 89 330 As can be seen from the above tabulated results, the corrugated containerboard made in accordance with the present invention exhibits almost twice the compressive strength as the conventional containerboard sold on the market when exposed to vapor or liquid phase water conditions.
While various specific examples of preferred procedure embodying the above invention have been described above, it will be apparent that many changes and modications may be made in the methods of procedure without departing from the spirit of the invention. It should, therefore, be understood that the methods of procedure set forth above are intended to be illustrative only and are not intended to limit the scope of the invention.
What is claimed is:
1. A highly water resistant linerboard which retains its strength under high humidity conditions comprising:
an upper web and a lower web positioned adjacent each other, Iboth webs containing a rosin sizing agent and the upper web in addition containing a wax `moistureproong agent, the upper and lower webs having impregnated only in the outer surfaces thereof l to 5 lbs. per thousand square feet of a partially cured starch extended phenol-formaldehyde resin wherein the molecular ratio of formaldehyde to phenol ranges from 0.9 to 3.0 moles of formaldehyde per mole of phenol.
2. Corrugated containerboard having high strength characteristics when exposed to high humidity conditions comprising:
a pair of spaced apart linerboards,
a wax impregnated corrugating medium positioned b..-
tween the spaced apart linerboards and adhesively adhered to the linerboards,
each of the linerboards comprising an upper web and a lower web positioned adjacent each other, both webs containing a rosin sizing agent and the upper web in addition containing a wax moistureproong agent, the upper and lower webs also having impregnated only in the outer surfaces thereof l to 5 lbs. per thousand square feet of a fully cured starch extended phenol-formaldehyde resin wherein the molecular ratio of formaldehyde to phenol ranges from 0,9 to 3.0.
3. A process for forming linerboard comprising:
depositing a first pulp material having a rosin sizing agent intermixed therewith on a moving means,
depositing a second pulp material having a rosin sizing agent and a wax intermixed therewith on top of the first pulp material,
5 pressing the first and second pulp material to form a References Cited lower web from the `rst pulp rnaterlal and an upper UNITED STATES PATENTS web from the second pulp material, drying the Webs, 2,178,358 10/1939 Howald et al. impregnating only in the outer surfaces of each of the 5 2 455299 3/1949 Wfichff 161-264 Webs 1 to 5 lbs. per thousand square feet of a starch 2,601,114 6/1952 Gluesple 16]246 extended phenol-formaldehyde resin wherein the molecular ratio of formaldehyde to phenol range-s MORRIS SUSSMAN Prmary Exammcr from 0.9 to 3.0, and
drying the webs at a sueient temperature to partially 10 U'S' Cl' X'R' cure the phenol-formaldehyde resin mixture. 156-210; ll-246, 264; 162-123, 127, 136