US3350261A - Paper stiffened with bark extractives and method of making the same - Google Patents

Description

United States Patent 3,359.261 PAPER STIFFENED WITH BARK EXTRACTIVES AND METHOD 0F MAKING THE SAME James R. Roberts, Paiatine, 111., and Arthur S. Gregory,

Tacoma, and Richard M. Morris, Longview, Wash., assignors to Weyerhaeuser Company, Tacoma, Wash, a corporation of Washington No Drawing. Continuation of application Ser. No. 236,142, Nov. 7, 1962. This application May 12, 1966, Ser. No. 550,880

11 Claims. (Cl. 162-117) This application is a continuation of Ser. No. 236,142, filed Nov. 7, 1962 and now abandoned.

This invention relates to the paper making art, and more particularly to a paper made from the common species of cellulosic materials and characterized by a high degree of stiffness and structural strength, and to the method of its manufacture.

Conventional methods of providing stiffened papers heretofore have involved the use of special cellulosic pulps which impart inherent stiffness to the paper, or the coating or impregnation of conventional paper stocks with special stiffening agents. However, these methods are economically disadvantageous in the following respects: The special cellulosic pulps are too costly for the limited degree of improvement which they impart to the paper. The special stiffening agents either are too costly or they present such problems as hazardous and difiicult application, unfeasible waste recovery, poor glueability, and fragility of the treated paper.

For example, sodium silicate has been employed as a low cost stiffening agent, but the treated paper is too brittle for such uses as corrugated medium. Additionally, the treated paper exhibits poor glueability and hence is not practical for such uses as liner for corrugated box material. Sulphur has been used as a stiffening agent, and although its unit cost is reasonably low the large amount require-d to be added to paper to achieve a reasonable degree of stiffness reflects an excessive cost to the finished product. Moreover, it is extremely hazardous and difficult to apply, its waste recovery is not economically feasable, and the treated paper exhibits poor glueability.

Synthetic resins of various types also have been employed as special stiffening agents, and while they impart to the paper increased stiffness, they tend to decrease flexibility and ease of corrugating and their high cost renders the product economically undesirable for general use.

Accordin ly, it is the principal object of the present invention to provide a stiffened paper from common species of cellulosic fibrous sources by a method which utilizes low cost raw material, which may be performed in conjunction with conventional types of paper making machinery at conventional production speeds, and which is capable of increasing the stiffness of paper without adversely affecting its strength or other desirable properties.

The foregoing and other objects and advantages of this invention will appear from the following detailed description.

In its broad concept, the present invention involves the impregnation of the cellulosic fiber of paper after formation of the sheet, with a treating solution consisting essentially of the alkaline soluble constituents of the barks of trees. Preferably, the solution is applied to one or both sides of a preformed sheet of paper stock, after the latter has been drained or dried, and the application is made in such manner as to effect pickup of from 0.5 to 15% or more solution solids by weight, dry sheet basis.

The method of this invention is applicable to any of the conventional paper making pulps derived from Wood,

3,35%,261 Patented 0st. 31, 1967 straw, bagasse, and like lignocellulosic materials. Further, it is applicable to pulps made by chemical, semichemical or mechanical methods.

The alkaline soluble constituents may be derived from the barks of coniferous or deciduous trees, the barks of the Douglas fir and Western hemlock being preferred for their availability.

In general, extraction of the bark may be effected with any alkaline solution and under all conditions of treatment which will achieve economically feasible extraction in good yield. In the preferred procedure, the alkaline bark extract is prepared by feeding bark in particulate form to a two stage countercurrent extraction process wherein it is subjected to the action of an aqueous alkaline solution for a time predetermined to dissolve the alkali soluble content of the bark.

The alkaline solution is prepared from a basic acting compound of an alkali metal or ammonia, preferably caustic soda, sodium carbonate, caustic potash, or ammonium hydroxide, in an amount ranging from 5 to 25% by weight, preferably 10 to 16% in the case of caustic soda, dry bar-k basis. The ratio of bark to aqueous media also is controlled to produce an alkaline extract having an organic solids concentration of from 5 to 25%.

The extraction is conducted at a temperature between ambient temperature and the boiling point of the extractor contents at atmospheric pressure, or at a higher temperature if super-atmospheric pressures are employed. Reaction time may vary from 10 to 180 minutes, preferably from 30 to minutes.

Upon completion of the reaction, the aqueous alkaline slurry is passed through a separator where the large insoluble bark solids are separated from the liquid. The insoluble bark fines carried with the liquid then are removed, preferably by centrifuging.

The foregoing alkaline extract contains a complex mixture of organic chemicals, which either are present as such in the original bark, or are derived therefrom by hydrolysis or other chemical reaction during the alkaline extraction, including the following classes of material.

Waxy components:

Salts of fatty acids Salts of hydroxy fatty acids Salts of phenolic fatty acid esters Neutral esters of fatty acids Long chain alcohols Sterols Non-waxy components:

Salts of monomeric and polymeric phenolic substances Salts of monomeric and polymeric phenolic acid substances The complex mixture comprising the alkaline extract may be employed per se for the purpose of the present invention. Alternatively, the mixture may be treated for removal of its wax fraction since it has been found that the wax-free fraction provides higher concora values than the untreated mixture. In either case the solution may be dried and the dried solids. redispersed in water to provide a treating solution.

The solids content of the treating solution may range from 5 to 25%, preferably about 15%, the upper limit being determined primarily by the viscosity of the solution at the application temperature. In general, the application temperature may vary between ambient temperature and the boiling point of the solution, preferably between F. and the boiling point which may be slightly above the boiling point of water. Higher temperatures with pressure are also possible. It is desirable that the solids content and temperature of the solution e in be as high as practicable, while providing a viscosity sufficiently low for eifective application.

It is also desirable that the paper sheet be formed from an aqueous slurry of fibers in such manner as to provide the characteristics of freeness, Cobb and porosity, consistent with its ultimate strength requirements, that give to the paper a high ability to pick up the aqueous solution. In this latter regard, solution solids pickup into the paper may range from 0.5 to more than 15% by Weight, dry fiber basis.

Since tests indicate that the solution solids penetrate into the cellulosic fibers, as well as collecting between the fibers, it has been found that a maximum increase in stiffness is achieved by applying the treating solution after the sheet has drained and partially dried. Accordingly, it has been found desirable to add the treating agent in the vicinity of the size press. Application of the solution may be effected by dipping the paper in the solution, or by depositing the solution upon one or both surfaces of the paper by means of spray nozzles or rolls.

Conveniently, the solution is applied intermediate the ends of the drier roll assembly, at a point where a sufiicient number of drying rolls still remain to achieve proper reduction in moisture content of the paper. Thus, for example, in a conventional drying assembly of about 50 rolls, the solution may be applied in the vicinity of the 40th roll.

It will be understood that the feed rate of the solution to the paper, to achieve a desired degree of pickup, varies with the web speed, characteristics of the paper sheet being formed, solids content of the solution, and other factors.

The treated paper may be employed per se for various commercial applications, such as liner for the production of corrugated box board. It may also be used as the corrugated medium, in which case the treated paper is passed through conventional corrugating apparatus. In this latter regard it has been found desirable to precondition the sheet with a greater amount of steam than ordinarily employed, to assure uniformity of moisture content throughout the sheet and to provide a slightly higher temperature in the sheet for most effective results at the fluting rolls.

The corrugated paper then is passed through conventional glue applying apparatus where glue is applied to the crests only of the corrugated medium. Face sheets then are applied to the opposite sides of the corrugated medium and the assembly pressed and cut to appropriate lengths.

The following examples are illustrative of the present invention:

EXAMPLE I Unbleached 38 pound and 42 pound kraft paper samples were treated at the size press with varying concentrations of an aqueous solution containing alkali soluble constituents of bark at 150 F. and, after conditioning at 50% relative humidity and 72 F. for a minimum of 24 hours, were tested for CLT improvement. The average results of these tests are given in Table I.

TABLE I CLT, lbs. Extract Solids Solids, Pickup, Web Post Percent by Percent by Speed, Control Test weight weight .p.m.

MD CD MD CD 4 EXAMPLE 11 Twenty six pound neutral sulfite semi-chemical paper samples were treated on one side with bark extract aqueous solution having varying percentages of alkali soluble solids, and comparative concora tests with control sheets were conducted without preconditioning. The test sheets then were corrugated on conventional corrugating apparatus at about 200 feet per minute and laminated with 42 pound unbleached kraft paper, both sides. After conditioning at 50% relative humidity and 72 F. for 24 hours the corrugated paper product was tested for flat crush and compression strength. The average results of these tests are set forth in Tables II and III.

TABLE II Solids Web Concora Test Extract Solids, Pickup, Speed, Percent by Weight Percent by f.p.m.

Weight Control Test 1. 5 800 68 82 4. 3 800 63 82 9. 3 800 64 68 2. 0 1, 48 78 2. G 800 48 78 3. 25 800 48 96 (applied both sides) TABLE III Flat Crush, psi. Test Corrugator Speed, t.p.1n.

Control Test 1 Not corrugated1nsutfieient material.

EXAMPLE III Twenty six pound neutral sulfite semi-chemical paper samples of varying porosity were treated with bark extract aqueous solution having from 15 to 18% by weight alkali soluble solids at to F., to determine the effect of porosity on the solids pickup and resulting concora. In one test, paper having a porosity of 206 seconds per 100 milliliters of air was treated at a web speed of 880 feet per minute. The solids pickup averaged 2.8% by weight and the concora 84 points. In a second test, paper having a porosity of 145 seconds per 100 milliliters of air was treated at a web speed of 900 feet per minute, resulting in an average solids pickup of 3.3% and a concora averaging 92 points. In another test, paper having a porosity of 110 seconds per 100 milliliters of air was treated at a web speed of 960 feet per minute, resulting in an average solids pickup of 3.5% and a concora averaging 95 points.

EXAMPLE IV Twenty six pounds neutral sulfite semi-chemical paper samples were treated with separate bark extract aqueous solutions both having about 12% by weight alkali soluble solids. However, one of the solutions was centrifuged to remove the insoluble bark fines. The paper treated with the solution containing the bark fines picked up an average of 4.04% by weight solids and, after conditioning at 50% relative humidity and 72 F. for 24 hours, had an average concora of 94 points as compared with 74 points for the control. The same paper treated with the solution in which the bark fines were removed, picked up an average of 5.14% by Weight solids and the conditioned sheet had an average concora of 116 points.

EXAMPLE v EXAMPLE VI To illustrate the eifect of applying the liquor solution at various points between the wet and dry ends of the paper, 26 pound neutral sulfite semi-chemical paper was treated with bark extract aqueous solution separately at the No. 5, No. 21 and No. 41 drier rolls, in a 51 drier roll assembly, by spraying the solution (11.6% alkali soluble solids) at a temperature of about 150 to 160 F. The results of this test are shown in the following table, the concora values being determined after conditioning at 50% relative humidity and 72 F. for 24 hours:

TABLE IV Treatment Location Solids Pick-Up, Concora Percent by weight Control 66. 68 No. 5 RolL- 4.03 70 No. 21 Roll. 4. 62 81 No. 41 R011 2. 93 88 In the above examples, the flat crush and box compression tests were made according to ASTM Standards D1225-54 and D-642-47 respectively. The CLT test is a well known test in the industry and consists of cutting a strip 6 inches long and /2 inch wide, clamping the same on edge between platens with A inch exposed and then compressing between the platens of an H & D tester and recording the pressure in pounds to crush the exposed edge. Likewise the concora test is well recognized in the industry, consisting of providing flutes in a strip originally 6 inches long and /2 inch wide, placing the corrugated strip on a strip of pressure sensitive adhesive tape and placing it between the platens of an H & D tester as mentioned above. The H & D tester and attachments are sold by Testing Machines, Incorporated, New York city, and is a standard piece of testing equipment throughout the industry.

From the foregoing it will be apparent that by the present invention papers produced from the common species of cellulose fiber material may be stiffened to a substantial degree at minimum cost, rendering the treated paper suitable for many commercial uses including the production of corrugated medium and liners. Furthermore, the treated paper of this invention may be run on corrugating machines at speeds up to 620 feet per minute which is the same as for untreated papers and greater than the speeds capable of being attained with other treated papers. Production costs are further minimized by enabling the process to be integrated into conventional paper making processes with minimum additional equipment and with no reduction in plant production speed. Production data also shows that in contrast to almost all other container boards containing additives, the waste treated paper of this invention can be easily repulped and reprocessed for further paper production.

It will be apparent to those skilled in the art that various changes may be made in the procedural steps, proportions of ingredients and other process conditions disclosed hereinafter, without departing from the spirit of this invention and the scope of the appended claims.

Having now described our invention, we claim:

1. The method of making stiifened paper, comprising forming the paper from an aqueous slurry of fibers, removing a substantial proportion of the water from the formed paper, applying to at least one surface of the paper an aqueous solution containing alkali soluble constituents of tree bark substantially free of alkali insoluble bark solids, and thereafter drying the paper.

2. The method of claim 1 in which said paper is corrugating medium, and including the additional step of fluting said paper.

3. The method of claim 1 in which said aqueous solution containing alkali soluble constituents of tree bark is substantially wax free.

4. The method of claim 3 in which said paper is corrugating medium, and including the additional step of fluting said paper.

5. The method of claim 1 in which said aqueous solution containing alkali soluble constituents of tree bark has a solids content ranging from 5 to 25% by weight, and in which 0.5 to 15% by weight, dry fiber basis, of said solids is added to said paper.

6. The method of claim 5 in which said paper is corrugating medium, and including the additional step of fluting said paper.

7. The method of claim 5 in which said aqueous solution containing alkali soluble constituents of tree bark is substantially wax free.

8. The method of claim 7 in which said paper is corrugating medium and including the additional step of fluting said paper.

9. The method of claim 1 in which said aqueous solution is at a temperature of from ambient to the boiling point of the solution.

10. The method of claim 9 in which said paper is corrugating medium and including the additional step of fluting said paper.

11. The product formed by the process of claim 1.

References Cited UNITED STATES PATENTS 1,280,400 10/1918 Clapp 162-11 1,828,029 10/1931 Marx 16293 X 2,698,233 12/1954 Lewis 162-93 X 2,781,336 2/1957 Zenczak 106163 2,823,223 2/ 1958 Steinberg 16293 X 2,840,138 6/ 1958 Johnston 117-158 FOREIGN PATENTS 587,237 11/1959 Canada.

DONALL H. SYLVESTER, Primary Examiner. HOWARD R. CAINE, Assistant Examiner.

Claims (1)

1. THE METHOD OF MAKING STIFFENED PAPER, COMPRISING FORMING THE PAPER FROM AN AQUEOUS SLURRY OF FIBERS, REMOVING A SUBSTANTIAL PROPORTION OF THE WATER FROM THE FORMED PAPER, APPLYING TO AT LEAST ONE SURFACE OF THE PAPER AN AQUEOUS SOLUTION CONTAINING ALKALI SOLUBLE CONSTITUENTS OF TREE BARK SUBSTANTIALLY FREE OF ALKALI INSOLUBLE BARK SOLIDS, AND THEREAFTER DRYING THE PAPER.