US2840138A

US2840138A - Wiltproofing paper and method of corrugating

Info

Publication number: US2840138A
Application number: US484582A
Authority: US
Inventors: Herbert N Johnston; Benson G Brand; Jr Willis B Lincoln
Original assignee: Inland Container Corp
Current assignee: Inland Container Corp
Priority date: 1955-01-27
Filing date: 1955-01-27
Publication date: 1958-06-24
Anticipated expiration: 1975-06-24

Description

WILTPROOFING PAPER AND METHOD CORRUGATING Herbert N. Johnston and Benson G. Brand, Columbus,

Ohio, and Willis B. Lincoln, Jr., Indianapolis, Ind., assignors, by direct and mesne assignments, to Inland Container Corporation (Indiana), Indianapolis, Ind., a corporation of Indiana N. Drawing. ApplicationJanuary 27,1955

Serial No 484,582

21 Claims. (Cl. 154 3 3.05)

This invention relates to. the treatment of paper and paperboard sheets or. webs hereinafter referred to as paper, with a molten, plasticized, resinous composition. The invention is concerned not only with the treating process and with the treated product, but also with the hereinafter-described treating compositions. 1 A problem of considerable importance to the paper and paperboard industry is the tendency of the paper to wilt under conditions of high humidity. The paper tends to absorb moisture from the air, with the result that the paper fibers soften and lose their stiffness. Obviously, the ultimate effect is a weakened paperboard structure which will not retain its shape undernormal handling in transit and storage.

Heretofore, various resinous compositions have been suggested for use in the molten state to impregnate paper. However, of the known resinous compositions, none have obtained commercial success because of one or more of several disadvantages. Substantially thorough impregnation of the paper must be obtained 'in order to effectively protect the fibers from the absorption of moisture and to effectively stiffen the sheet. The ability of the molten resinous composition to penetrate and impregmate the paper is related to the viscosity of the composition. Accordingly, the resinuos composition in its molten state must have a viscosity such that it will penetrate and become impregnated or embodied in the paper. Increasing the temperature of a moltenfresin, of course, decreases its viscosity. However, for paper impregnation pur poses, the temperature of the molten resin is seriously limited to a low maximum temperature. H The temperature of the molten resin should not exceed that temperature at which the paper will char or otherwise become heat-damaged. The disadvantage of many of the known molten resinvimpregnating compositions is that the resin compositions have high-melt temperatures and also highmelt viscosities. Thus, in order to obtain substantial wilt-proofing of paper, the molten resin composition must have a low-melt temperature and a viscosity at low remperature which will permit rapid. and substantially than ICC ough impregnation or penetration of the paper by the molten resin composition.

The impregnating material should not form a glossytype coating on the surface of the paper. In thejjpjroduction of corrugatedpaperboard, solid fibreboard and related products, it is essential that the surface of the impregnated paper be compatible with a combining adhesive subsequently used in the production of manufactured items. That is, the impregnated paper should have the fibers exposed so that the paper will accept the ad hesive and bind itself to other paper liners.

A further disadvantage of some impregnating agents is that the presence of the impregnating agents prevents the repulping of the impregnated paperfor re-use.

The composition of this invention, comprising fatty acid plasticized, pine wood-type resin, hasbeen fou'ndto give "excellent" wilt-resistant properties to paperboard and paper. The plasticized resin composition in amolten state is applied to the surface of the paper in the form of a coating, and then heat treated to cause th'epl'asticized resin to impregnate and penetrate into the paper without the formation of a glossy-type coating. Accordingly, an object of 'this invention is to provide a wilt-resistant paper. A further object is to provide a 'pl'asticizedres'in treated paper, which is characterized by increased rigidity, even when in contact with an atmo phe're 'o'f high humidity. An additional object of this invention is toobtain' animpregnated paper which-does not have 'a' glossy-type coating and which is compatible with combining or laminating adhesives. A further advantageous feature is that the impregnated paper of this invention is 'capableof being repulped for re-use. As will 'become apparent from the following disclosure, an object realized is the'a'pplication of the molten, plasticized resin to the paper at relatively low temperatures, which will 'notchar or otherwise heat-damage the paper. It.will be obvious to those versed in the paper-making and paper-converting arts that the original strength or rigidity of untreated paper will be a determining factor, together with other factors, governing rigidity and strength characteristics of the treated sheet of paper.

Other objects and advantages will become apparent from the following detailed disclosure and examples. 1

In the following table are set forth examples of various compositions of the plasticized resin of the present'inven tion. The paper used in accordance with these examples is that paper which is used in the manufacture of corrugated fibreboard commonly known as semi-chemical corrugating material or medium. Paper made byother well known processes such as kraft'paper, straw paper,

repulped waste papers, etc., may be used. The percentage values given in the table are based upon percentage by weight.

3 4; Table Formula Plastletaehleroent composition Test data com osition Ex. Satu- Penetration Concora medium test Per- Per- 7 rated Flow cant cent Oa- Cap- Lau- My- Pal- Ste- Oleic Lin- Linofatty point, resin lasllt. rlo rio rlstic mltlc arlo olelo lenlc acid Per- F. Imme- R. 11., R. H.,

ticker mix- Sec. cent dlate 50% 85%,

mm 3days 22 75 3 3. 70 179 98. 7 83. 3 38. 7 53 42 3.00 to 4.00 80-85 187 99.3 83.7 37.0 54 43 3 3. 00 75 178 108. 7 86. 9 52. 0 54 4.3 3 3.00 80 192 99.7 79.8 47.7 54 43 3 3. 00 95 203 108. 7 86. 9 51. 0 54 43 3 3. 00 70 186 96. 3 77. 1 50. 7 54 43 3 3.00 60 200 78.3 62.7 41.7 54 43 3 3.00 40-50 235 7 90.7 72.6 31.3 92 6 2 3. 43 90 170 89. 3 81. 7 35. 3 60 36 4 3.62 85-90 186 111.0 86.3 43.0 32 64 '4 2. 72 80-90 196 98.0 87. 3 40. 7 23 75 2 2. 64 60-70 190 101. 3 78. 3 41. 3 8 90 2 2. 62 85 200 100. 3 95. 7 37. 3 3 2 30 16 50 2. -70 172 58. 0 50. 0 27. 5 4 91 5 2. 68' '90 158 96. 0 96. 3 45. 0 8 7 17 9 2- 6 2 3.75 50 136 54.8 62.4 27.8 50 48 2 3.00 6070. 184 57.0 48.3 28.0 r 38 6 1 55 2.69 50-60 169 63.6 58.0 33.4 100' 2.62 80 90 187 93.7 84.3 38.3 55 45 2.93 80-85 188 96.3 86.7 39.7 2.52 50 168 67.3 53.7 28.0 54.3 43.4 26.0

in examples is an extracted pinewood-type resin, hereinafter referred to as substantially petroleumhydrocarbon insoluble pine wood resinfi This resin is that which isisolated from pine wood in the following'mannerz The pine wood, which may or may not have" beens'tearne'd to remove volatileconstituents, suchasturpentine and; pine oil, is extracted with a coal tar hydrocarbon-such as benzene or toluene, and the ex- ;tractis then freed of'yolatile constituents, leaving; aresinous residue consisting of a mixture of wood rosin and therresin in the present composition; The rosin is dissolved and; removed fiomthe residue by extraction with a petroleum hydrocarbon, such as gasoline. .The' resinous residue remaining after the petroleum hydrocarbon extraction islowinabietic acid. This resin,.low in abietic acid,

1.8 th s liwhich comprises f the resin employed accdrdcommas; Wilmington, Delaware.

The fatty acids and mixtures of fatty acids function as a plasticiner or .introfier for the resin. The-fatty acid placticizing agents enabletheresin to quickly penetrate the surface of the paper and cause substantially thorough impregnation of the resin throughout thepaper at relatiYely low. temperatures.- The preferred fatty acids useful for theplasticization or introf action ofthe substantially petroleum hydrocarbon insoluble pine wood resin for the purposes of this invention are the saturated andunsaturated fattyIacids having from eight to eighteen carbon atoms. As shown in the table. the fatty "acid content of the compositions may vary'from 10 to 70 percent of the total, by weight, with. the balance being the substantially petroleum hydrocarbon insoluble pine wood resin. For the reasons which will appear below, the. preferred composition is that which has a fatty acid content of approximately to 50 percent. p

The plasticized substantially petroleum hydrocarbon insoluble pine wood resin is applied to the paper in a molten'. state. Plasticization of i the resin may be accomplished by heating'a'mixture of the unmelted resin and thefatty acid plact icizing agent. The mixture is stirred sufliciently to obtain a uniform dispersion of the plasticizing agent in the resin. Themolten plasticized resin is maintained at a temperature below that which will Chat or burnthe paper, preferably about 325 F. to 33 5- .F., although temperatures as high as 400 F. to 415 F. have been used. Afterthe plasticized resin is applied to the surface of the paper in the form-"of a coating, the coated paper is heat treatedto cause the plasticized resin to become impregnated in the paper. Again, in the practice of this invention, the temperature of the heat-treating step need, not be in excess of that temperature which will heat-damage the paper, but, of course, should be above the flow-point. temperature ofthe plasticized resin. In the examples cited in the table, a method using a minimum of operational steps was used. In the'method used, the paper is passed between two hot rolls. The lower roll is in contact with, or partially submerged in, a molten bath of the plasticized resin. The lower roll serves to'pick up the molten plasticiz'ed resin and coat the side of the paper which is passed in contact with the lower roll. The'upper roll may be used to cause partial impregnation 0f the plasticized resin as it is coated on thepaper by pressing the paper upon the lower pick-up roll. The paper maythen be continuously brought into contactwith another heated roll. This subseqeunt contact with the heated roll constitutes the heat-treating step which causes the impregnation of the plasticized resin into the paper. The impregnated paper does not have a glossy coating over the surface. The surface of the paper advantageously retains its compatibility with combining or laminating adhesives.

This example describes an application method for coating and impregnating one side of the web under treat? ment. It will be understood that provision for application of the molten, plasticized; resinous impregnating eomposition to either one side or both sides of the web receiving impregnation shall be within the scope of this ve i n. i

In the table, Examples 1 through 13 show a variety of mixtures of palmitic, stearic, and olcic acids as' plasticizing agents combined in various proportions with the substantially pe troleum hydrocarbon insoluble resin. Examples 14 through 16;are directed to'plasticizing agents containing lower fatty acids, thelowest fatty acid having a minimum of eight carbon atoms. Examples 17 and 18 are directed to plasticizing agents containing the higher fatty acids, the'highest fatty acid having a maximum of eighteen carbon atoms. The plasticizing agents of Examplesi'17 and 18 also containan amount of miscellane to eighteen carbon atoms. The fatty acids of Example 17 are commonly known as tall oil fatty acids. The fatty acids of Example 18 are those derived from distilled palm oil and are commercially available under the trade name Emery 640, marketed by Emery Industries, Inc. The plasticizing agent of Example 19 is rubber grade stearic acid and is available from a number of commercial sources, such as General Mills, Inc. Example 20 shows a plasticizing agent consisting of palmitic and stearic acids in about equal proportions. Example 21 is illustrative of a plasticizing agent consisting of a mixture offatty acids present in tallow, commonly known as tallow fatty acids. Example 22 is an untreated sample of the corrugating material. Its wilt-resistant characteristics are given for purposes of comparison with the same paper treated in accordance with the present invention.

Reference to the test-data columns'shows the rapidity at which the plasticized resin composition penetrates and impregnates the paper. The time of penetration is determined by pressing a 4-inch by 6-inch piece of paper as it comes from the pick-up roll against a stationary roll which is maintained at a temperature of 330 'F. This temperature is well within the range of temperatures which will not char 'or otherwise heat-damage the paper. The degree or percent of penetration of the plasticized resin into the paper is determined by measuring the extent to which the impregnating material soaks or migrates into a sheet of paper. For example, a 10-point sheet (.010- inch thick) which is impregnated in accordance with the present'inventionto a depth of 8 points (.008'inch) has an 80 percent penetration of the plasticized resin.

In addition to functioning as a plasticizing agent for the substantially petroleum hydrocarbon insoluble pine wood resin, the fatty acids affect a lowering of the flowpoint temperature of the resin. In comparison with the values of the table, the flow point temperature of the unplasticized resin is 240 F. A fatty acid content of 30 to 50 percent provides an adequate lowering of the melt temperature to give a satisfactory degree of impregnation for wiltproofing the paper.

The temperature at which the plasticized resin will begin to flow is determined by a modified Columbia method. In this method a 1-inch test tube is supported in the center of a beaker filled with mineral oil. A thermometer bulb is two-thirds coated by dipping into the molten plasticized resin, and removing at a slow, even rate. When cool, the thermometer is then suspended in the center of the test tube. The mineral oil is then heated, and the temperature at which a drop of the plasticized resin falls from the thermometer bulb is recorded as the flow point. v

The wilt-resistant and crush-strength properties of the plain and impregnated corrugating material paper 'were determined by the Concora Medium Test. Essentially, this test consists of cutting an accurate 6-inch by /2'- inch specimen and then corrugating the specimen through a fluter. The corrugated sample is placed on a rack with flutes matching the configuration of the sample. A comb is placed over the sample to hold it in place and a strip of A-inch wide tape is adhered to it. Then the comb is removed and the resulting sample strip of socalled single face is placed between the platens of" a fiat crush tester. The force in pounds necessary to crush the sample is the test result. This testing procedure is more particularly described in the article -entitled A new test for corrugating medium, by F. D. Long and G. G. Maltenfort, published in Fiber Containers and Paperboard Mills, pp. 86 to 92 (December 1952). Specimens of each of the examples were subjected to flat crush testing immediately after Concora fiuting and single face sample fabrication. Other specimens of each of the examples were tested after 1 days exposure to 5 0 percent relative hum'idityto bring "the -specimens to a stateiof moisture equilibrium therewith. In addition, specimens of each of these examples were tested after :three' days exposure to the extreme condition of percent relative humidity. The values for these tests are set forth in the last three columns of the table. The Concora 'Medium Test results for untreated corrugating material paper. are recorded as Example 22. Comparison of these values for Examples 1 through 21 with the values for the untreated corrugating material paper of Example 22 shows the improved wilt-resistant properties of the paper treated with the fatty acid plasticized resin of the present invention.

Examples given in this specification are illustrative of the plasticized resinous impregnating composition dis closed herein, but are not to be construed as limiting said impregnation composition.

It will be understood that impregnation or treatment of paper components subsequently to be combined or laminated into corrugated fibreboard and/or solid fibreboard and utilized as such shall be within the scope of this invention. Conventional use of the impregnated paper component in corrugated fibreboard shall be as the inner component of the fibrebo'ard known as corrugated material, but the other components can receive like treat merit also. The commercial material known as solid fibreboard differs from corrugated fibreboard in that all plies of the solid fibreboard are in intimate continuous contact one with the other. Any one or all of the component paperboard plies of fibreboard can be im pregnated by methods disclosed herein prior to final com bination as the said solid fibreboard.

In summary, it is seen that the fatty acid plasticizing agent enables the resin to easily and quickly penetrate into the paper. The process of impregnating the paper involves a minimum of procedural steps and, therefore, has the advantage of being adapted to use with existing commercial equipment. The fatty acid plasticized substantially petroleum hydrocarbon insoluble pine wood resin imparts increased wilt-resistant properties to the paper as evidenced by the increased strength and rigidity of the treated paper under conditions of ex'posure.t0 normal and relatively high humidity.

What is claimed is:

1. The method of imparting wilt-resistant properties to paper comprising coating the paper with molten plasticized resin, said plasticized resin comprising from about 30 to percent of substantially petroleum hydrocarbon insoluble pine wood resin and the balance at least one fatty acid as a plasticizer, and thereafter contacting the coated paper against a heated surface to impregnate the paper with said resin.

2. The method of imparting wilt-resistant properties to paper comprising coating the paper with molten plasticized resin, said plasticized resin comprising from about 30 to 90 percent of substantially petroleum hydrocarbon insoluble pine wood resin and the balance at least one fatty acid having from 8 to 18 carbon atoms as a plasticizer, and thereafter contacting the coated paper against a heated surface to impregnate the paper with said resin.

3. The method of imparting wilt-resistant properties to paper comprising coating'the paper with molten plasticized resin, saidplasticized resin comprising from about 30 to 90 percent of substantially petroleum hydrocarbon insoluble pine wood resin and the balance stearic acid as a plasticizer, and thereafter contacting the coated paper against a heated surface to impregnate the paper with said resin.

4. The method of imparting wilt-resistant properties to paper comprising coating the paper with molten plasticized resin, said plasticized resin comprising from about 30 to 90 percent of substantially petroleum hydrocarbon insoluble pine wood resin and the balance a mixture of lauric, myristic, and palmitic acids as a plasticizer, and

30 to 90 percent of substantially petroleum hydrocarbon insoluble'pine wood resin and the balance tallow fatty acids as a plasticizer, and thereafter contacting the coated paper against a heated surface to impregnate'the paper withsaid'resin. A t a 6. Ina methodfof makingcor'rugating material for corrugated fibreboard construction, the step of imparting wilt-resistant properties to said corrugating material comprising impregnating paper with molten plasticized resin, said plasticized resincomp'rising from "about 30 to 90'percent of substantially petroleum hydrocarbon insoluble pine wood resin and the balance at least one fattyacid as a plasticizer, and corrugating the impregnated P e -.4 J I 7.-In a. method of making corrugating material for corrugated fibreboard construction, "the step of imparting wilt-resistant propertiesfto said corrugating material comprising impregnating paper with molten plasticized resin, said plasticized resincomprising from about 30 to paper, said plasticized' resin comprising from about 30.

to 90 percent of substantially petroleum hydrocarbon insoluble pine wo od resin and the balance at least one fatty acid having fron i 8 to 18 carbon atoms as a plasticizer. 10. A corrugating material having improved wilt-resist ant properties comprising plasticized resin-impregnated paper, said plasticized resin comprising from about 30 to 90 percent of substantially petroleum hydrocarbon insoluble pine wood resin and the balance stearic acid as a plasticizer. t

11;? Acorrugatingmaterial having improved wilt-resistant properties oomprising plasticized resin-impregnated paper, said plasticized resin comprising from about 30 to 90 percent of substantially petroleum hydrocarbon insoluble pine wood resin and. the. balance a mixture of lauric acid, myristic acid, and palmitic acid asa plasticizer. r

12. A corrugating material having improved wilt-resistant propcrties comprising plasticized resin-impregnated paper, said plasticized resin comprising from about 30 to90 percent of substantially petroleum hydrocarbon insoluble pine wood resin and the balance tallow fatty acids as a plasticizer.

l3. A'papcrboard sheet suitable for use as at least one of the facing components of corrugated fibreboard, said sheet comprising plasticized resinimpregnated paperboard, said plasticized resin comprising from about 30 to 90 percent of substantially petroleum hydrocarbon insoluble pine' wood resin and the balance at least one fatty acid as a plasticizer. V t

1 14. A paperboard sheet suitable for use as at least one of 'thefacing. components of corrugated fibreboard, said sheet having increased wilt-resistant properties comprising plasticized resindmpregnated paperboard, said plasticized resin comprising from about 30 to 90 percent of substantially petroleum hydrocarbon insoluble pine wood resin and the balance at least one fatty acid having from 8 to 18 carbon atomsasa plasticizer. I 15. Paper suitable'for inclusion as at least one of the components-of fibreboard, said paper comprising plasticized resin-impregnated paper, said plasticized 'r esin comprising from about to 90 percent of substantially petroleum hydrocarbon insoluble pine wood resin and the balance at least one fatty acid as a plasticizer.

16. Paper suitablefor use as at least one of the components of fibreboard, said paper having increased wiltresistant properties comprising plasticized resin-impregnated paper, said plasticizedv resin comprising from about 3010 90 percent of substantially petroleum hydrocarbon insolublepine wood resin and the balance at least one fatty acid having'from 8 to 18 carbon atoms as a plasticizer. r a

17. A hot-melt ,resinous composition for wilt-proofing paper or paperboard comprising from about 30 to 90 percent of substantially petroleum hydrocarbon insoluble pine wood resin and the balance at least one fatty acid as a plasticizer, said composition characterized by a lowmelt viscosity below that of said pine wood resin without said plasticizer-and the ability to rapidly penetrate and impregnate the paper. I

18. A hot-melt resinous composition for wilt-proofing paper or paperboard comprising from about 30 to 90 percent of substantially petroleum hydrocarbon insoluble pine wood resin and the balance at least one fatty acid having from 8 to 18 carbon atoms as a plasticizer, said composition characterized by a low-melt viscosity below that of the said pine wood resin without said plasticizer and the' ability to rapidly penetrate andimpregnate the paper. a

19. A hot-melt resinous composition for wilt-proofing paper or paperboard comprising from about 30 to 90 percent of substantially petroleum hydrocarbon insoluble pine wood resinand the balance stearic acid as a plasticizer, said composition characterized by a low-melt viscosity below that of the said pine wood resin without said plasticizer and the ability 'to rapidly penetrate and impregnate the paper.

.20. A hot-melt resinous composition for wilt-proofing paper or paperboard comprising from about 30 to percent of substantially petroleum hydrocarbon insoluble pine wood resin and the balance a mixture of laun'c, myristic, and palmitic acids as a plasticizer, said composition characterized by a low-melt viscosity below that of the said'pine wood resin without said plasticizer and the ability to rapidly penetrate and impregnate the paper. 21. A hot-melt resinous composition for wilt-proofing paper or paperboard comprising from about 30 to 90 percent of substantially petroleum hydrocarbon insoluble pine wood resin and the balance tallow fatty acids as a plasticizer, said resin composition characterized by a low-melt viscosity below that of the said pine wood resin without said plasticizer and the ability to rapidly penetrate and impregnate paper.

, References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,840,138 June 24, 1958 Herbert NA Johnston et a1,

It is herebfii certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5 line '75, for ''after 1 day's exposure to 50 percent" read after exposure to 50 percent n Signed and sealed this 9th day of September 1958,

( SEAL) Attest:

KARL H-o AIEINE v ROBERT C. WATSON \ttesting Officer Commissioner of Patents

Claims

7. IN A METHOD OF MAKING CORRUGATING MATERIAL FOR CORRUGATED FIBREBOARD CONSTRUCTION, THE STEP OF IMPARTING WILT-RESISTANT PROPERTIES TO SAID CORRUGATING MATERIAL COMPRISING IMPREGNATING PAPER WITH MOLTEN PLASTICIZED RESIN, SAID PLASTICIZED RESIN COMPRISING FROM ABOUT 30 TO 90 PERCENT OF SUBSTANTIALLY PETROLEUM HYDROCARBON INSOLUBLE PINE WOOD RESIN AND THE BALANCE AT LEAST ONE FATTY ACID HAVING FROM 8 TO 18 CARBON ATOMS AS A PLASTICIZER, AND CORRUGATING THE IMPREGNATED PAPER.