US2601114A - Paperboard product and process for making same - Google Patents

Description

June 17, 1952 w. F. GILLESPIE 2,601,114

PAPERBOARD PRODUCT AND PROCESS FOR MAKING SAME Filed Jan. 8, 1949 INVENTOR: wfi

HIS ATTORNEYS.

Patented June 17, 1952 PAPERBOARD PRODUCT AND PROCESS FOR MAKING SAME Wilbur F. Gillespie, Bogalusa, La., assignor to Gaylord Container Corporation, St. Louis, Mo., a corporation of Maryland Application January 8, 1949, Serial No. 69,955

6 Claims. 1 This invention relates to a process of preparing new paperboard products of high wet strength, abrasion and grease resistance, especially designed for the fabrication of multiple trip carriers including containers for bottled beverages prepared by a special process combining external and internal treatments. This process provides, among other improvements, an outer board surface of high resistance to abrasion, frictional losses, moisture and grease penetration under the most rigorous conditions of service.

An object of the invention is to provide a combined board having a wet Mullen strength at least 50% of its 'dry strength, and an outer surface highly resistant to abrasion or scufllng under both wet and dry conditions and possessing excellent printing properties.

Another object is to provide a linerboard having its outer or exposed surface resistant to soiling by grease, dirt, and other extraneous substances so that the attractive appearance of shipping containers manufactured therefrom will be preserved during their normal life.

Another object of the invention is to provide a solid fibre laminated board suitable for fabricating multiple trip beverage carriers having a minimum dry Mullen test of 550 pounds per square inch, and a Wet Mullen test of not less than 300 pounds per square inch after immersion in Water at 75 F., for twenty-four hours according to the JAN- 108 specifications of the Army and Navy and an outer or exposed surface of very high resistance to abrasion or scuffing under both wet and dry conditions, combined with excellent p-rintability and soiling resistance.

Further objects of the invention will appear from the description and example of the process and the appended claims.

The use of fibre containers suitable for transporting bottled beverages such as beer, soft drinks, and the like, from the manufacturers or bottling plants to the dispensers and consumers of such products, and which may be returned to the beverage supplier for ten to fifteen or more refillings and return trips, is extensive and rapidly increasing. Such containers are known in the trade as multiple trip carriers. Fibre boxes for this purpose have important advantages over metal strapped carriers made of wood. For example, the standard twenty-four 12-oz. fibre boxes are from four to eight pounds lighter in weight than wooden boxes of similar carrying capacity, with resulting savings in transportation expense. They have the additional advantages of eliminating re-cocpering costs and the personal injury hazard involved in the use of metal strapped wood cases.

Present multiple trip fibre carriers are ordinarily constructed of 3 to 5-ply laminated solid fibre blanks, comprising inner filler sheets and two liners. The natural lively color of kraft board imparts an attractive pleasing appearance to the package. The walls of the case provide an excellent means for printing the manufacturers advertising matter.

The outer liner of the solid fibre sheet on present multiple trip carriers is usually coated with paraffin or similar oil or wax base material to provide partial resistance to moisture penetration under high relative humidity and the usually weathering conditions to which such carriers are necessarily subjected. Such coatings, however, have very slight resistance to abrasion so that in the course of the severe wear and tear to which multiple trip carriers are subjected, the protective coating usually cracks and becomes partially scuffed from the corners and especially the bottom of the box, thus destroying any moisture resistance of the container, which is then subject to rapid deterioration under conditions of high relative humidity or partial exposure to Water.

Parafiin or similar oil or wax base coatings detract from the brilliancy of both printing and the attractive natural color of the board, thus adversely aifecting the advertising value and. appearance of the case. Such coatings are greasy to the touch and have a pronounced tendency to pick up foreign material, dirt, and the like, so that the case, including the printing, soon becomes unsightly and unfit for further use. Another objection to paraflin and similar coatings is their tendency to rub off and soi1 any material with which they come in contact, including clothing and other fabrics.

when loaded with beverage products to withstand crushing or collapse when stacked ten or twelve high in trucks or railroad cars. In addition, sufficient structural rigidity of the case should be maintained under extreme weather conditions during transportation and other con-' ditions incident to normal use to prevent failure or collapse. Ordinarily carriers of the usual construction, when exposed to high relative humidity or to water for any appreciable length of time, will undergo ply separation of the laminated solid fibre board. This in turn promotes absorption of water by capillary attraction throughout the fiber structure with consequent loss of rigidity and permanent damage to the container.

Thus a solid fibre laminated board, suitable for fabrication into serviceable multiple trip carriers, must meet several exacting physical requirements to insure satisfactory functioning of the boxes fabricated therefrom throughout their normal life in multiple trip service.

This invention teaches a process of preparing a new paper board product comprising a series of balanced specific treatments applied to selected cellulosic fibres during the process of sheet formation, calender finishing, and lamination into multi-ply board, whereby specific physical properties are imparted to the combined sheet. Each of the treatments is essential and the combination of the coordinated series practically overcomes all of the foregoing objections and deficiencies found in present multiple trip carriers constructed of the best commercially available solid fibre board.

The linerboard of this invention may be formed of chemical pulp derived from long, strong fibered wood, carefully digested and refined for producing maximum strength properties. It may be of any desired weight and caliper, depending upon the purpose and use of the containers manufactured therefrom. For example, the liner for combined fibre-board suitable for multiple trip bottle carriers may be an 80 pound, .022 caliper sheet containing substantially 100 percent of said high strength chemical pulp. During the manufacturing process a rosin size is applied to the liner in sufiicient quantity to insure an average absorption number not exceeding 350 according to the standard method hereinafter described.

The next step in the process is to concentrate an abrasion resistant and wet strength imparting resin composition in one or more of the outer plies of the linerboard. A suitable resinous composition for this purpose is a melamine formaldehyde condensation product, such as that known in the trade as Parez #607. Other resinous compositions, well known to those skilled in the art, such as, urea formaldehyde, will also give satisfactory results. These other compositions may be used in appropriately varying proportions, by weight, to obtain results similar to those with the use of the melamine formaldehyde condensation product.

I have discovered that by concentrating a sufficient amount of the resinous composition in one or more of the outer plies of the linerboard, a wet Mullen test of the laminated board at least percent of the dry Mullen strength will be assured. The introduction of this resinous composition as described, substantially supplements the natural bonding of the outer fibrous layers of the sheet, thereby greatly increasing the strength, toughness or scuff and abrasion resistance of the board in the outer surfaces, that is, in the region which is subjected to the most severe frictional wear when the laminated sheet is fabricated into a container.

I am aware that the addition of melamine and other wet strength abrasion resistant type resins to the furnish in paper-making have been advocated, but the method of applying such resins has been to uniformly disperse them throughout the sheet, whereas in my invention, the resins are concentrated in or near the surface of the sheet to attain suitable high wet Mullen strength and abrasion resistance in only those areas where these properties are essential for the objectives of my invention. The concentration of resin in the outer plies of the liner acts as a partial barrier to lateral water penetration into the remaining plies of the liner. This step of the process in combination with a special calender treatment and a water insoluble bonding of the liners and fillers into the combined board, to be hereinafter described, in turn reduces the water penetration into the inner filler sheets substantially so that a high wet strength of the laminated board is obtained with the use of a relative very small amount of resin.

This novel means of obtaining the high wet strength objective without incurring the prohibitive cost of distributing a sufficient quantity of the resin throughout the liner to obtain equivalent results, is one of the important features of my invention. It furthermore fulfills another important objective of concentrating the abrasion resistant resin in just that part of the liner which is subject to severe frictional damage, namely, the outer surface.

A further treatment is given to the linerboard at the calender stacks to improve the water and grease resistance and still further improve the resistance to abrasion or scuiiing. A unique combination of chemicals for this purpose, constituting an important feature of the invention, consists of a thin boiling starch, dimethylol urea and polyvinyl alcohol in an aqueous solution. Without being able to precisely define the chemistry involved in this combination which imparts unexpected, valuable and essential properties to the outer surface of the liner, it is believed that the thin boiling starch re-acts with the dimethylol urea to form a compound highly resistant to abrasion and moisture resistance, in these respects supplementing the properties imparted to the board by the previously described resin treatment, and the polyvinyl alcohol component increases the resistance to grease penetration and soiling, thus preserving the original attractive appearance of the linerboard.

In addition, the calender treatment with the described combination of chemicals imparts a smooth finish of excellent printability to the surface of theliner. The board retains its characteristic bright color in contrast to the inferior printing surface and unattractive color of the board which characterizes the paraffin coating usually applied to board for containers of the class described.

The next step in the process of preparing fibreboard suitable for multi-trip carriers is to prepare a filler sheet which may be, for example, a pound, .025 caliper board, with a furnish controlled to meet the required test specifications, A rosin or wax size or a combination of sizes is applied to the filler sheet in sufficient quantities to insure an absorption number of not more than an average of 350.

Filler sheets and an inside and outside liner, prepared as described, are combined into a multiply solid fibre board with an adhesive composition capable of formingan irreversible pletely' water insoluble gel.

After submergingin water for a minimum of twenty-four hours, according to the JAN-P-108 specifications of the Army and Navy, this laminated sheet will have a Mullen test at least of the value before submergence and will show no separation of the component plies. It has an abrasion resistance even when wet several times that of ordinary solid fibre board so that shipping containers fabricated therefrom will withstand far more wear and tear over Wet concrete floors, for example, and other severe conditions of use, than boxes made from the usual quality of solid fibre board.

The combined sheet has a dry G. puncture test of at least 550 inch ounces and a test after submergence in water of not less than 450 inch ounces, or 80% of the dry. It has a coefficient of friction within the range found to be satisfactory for commercial purposes, namely, .275 to .350 determined by the method hereinafter described.

Multi-trip carriers made from the combined board described have a useful life'at least 50% greater than boxes made from the best commercial solid fibre grades now available. This feature insures important economies to the users of such containers.

and com- Furthermore the special finish to the exposed surface of the board preserves the original natural color so that the attractive appearance of the carrier is maintained to a high degree even after re-use twenty or more times.

The liner produced by the process of this'invention may be bonded to corrugating medium to form corrugated board having similar enhanced properties. It may also be used in the manufacture of other laminated products with correspondingimproved resistance to frictional losses, and increased useful life under extreme conditions of relative humidity.

Having thus set forth the general aspects of my invention, I will describe one form by an example for producing a solid fibre boardsuitable'for fabricating multi-trip bottle carriers of greatly improved quality. It must be understood that this example is illustrative of one form of my process and that my invention is not limited thereto but may be varied therefrom by the use of resinous materials other than melamine formaldehyde condensation products, and materials giving equivalent results in the calender treatment of the linerboard, and laminating adhesive compositions other than soya protein, in quantities, concentrations, etc., falling within the purview of the appended claims, may be employed if desired.

In the accompanying drawings which form a part of this specification,

Fig. 1 represents a simplified diagrammatic side elevational view, partly in section, of a cylinder machine illustrating my process for my paperboard product. i

Fig. 2 represents a simplified diagrammatic side elevational view partly in section of a Fourdrinier machine illustrating my process for my paperboard product.

The cylinder machine includes whipper I, cylinders 2 for liner stack, cylinders 3 for filler stack, couch roll 4, press sections 5, dryer sections 6, first calender stack 1, calender dryers 8, and second calender stack 9.

The Fourdrinier machine includes headbox l0, breast roll H, table rolls l2, dandy 'roll l3,

suction boxes [4, return wire roll l5, wire [6, suction couch roll ll, lump breaker roll l8, dryer sections l9, first calender stack 20, calender dryers 2|, and second calender stack 22. The machines hereinbefore described are of a well known type and it is considered unnecessary to illustrate them in detail.

Following is an example ofthe preferred practice in carrying out my invention:

Step 1.An pound,-.022 caliper linerboard sheet. testing 150 pounds per square inch, is prepared on a cylinder machine from high strength sulphate pulp derived from strong, long fibered wood, sized in the usual manner with '75 gallons of a 5% solids rosin size solution per ton of board.

The amount of size specified will insure an average absorption number of the board of not more than 350.

The pH of the'stock is adjusted to between 4.0'and 6.0.

Step 2.--The linerboard consists of five. (5) plies. The two outer plies are treated with from 1% to 5%, by weight, of a melamine formaldehyde resin, such as that known by the trade name of Parez #607. The resin solution enters with the stock at A in Fig. 1. I have found that 3.5% of the resin gives very satisfactory results. When the board is prepared on a Fourdrinier machine, the required amount of resin enters with the stock at the secondary headbox B in Fig. 2.

The resin is prepared for use by mixing in a hydrochloric acid-water solution so that a final composition contains about 12% of the resin, by weight, and has a molar ratio of hydrochloric acid to the melamine of approximately 0.8. After thorough mixing, the solution is allowed to age for approximately twelve hours at its mixed concentration. It is then metered to the stock slurry at its mixed concentration or further diluted with water if desired. In the case of the cylinder machine, the point of addition to the stock should be as near to the cylinder headbox as possible. In Fourdrinier machine application, the addition is made to the stock going to the secondary headbox, or in the secondary headbox. At the customary temperature to which the board is raised as it passes through the driers, the resin is polymerized or cured, thereby increasing the natural bond of the fibers in the two outer plies of the board. This increased bonding of the outer fibers results in an overall increased tensile strength of the board, greatly increased resistance to abrasion or scuffing and at least a increase in the wet Mullen strength of the treated board as compared to the wet Mullen strength of the untreated board.

Step 3.As an additional protection to the surface of the liner, and to impart improved moisture and grease resistance, a novel chemical composition is applied to the board on the calender stacks at C in Fig. 2, and at a corresponding point D in Fig. 1 in the case of a cylinder machine. The unique treatment comprises the reaction product of a combination of a thin boiling starch, which is a product well known to those skilled in the art, dimethylol urea and polyvinyl alcohol.

The composition is prepared as follows:

Water gals 75 Thin boiling starch, an example of which is Starch' R supplied by Penick and Ford lbs 100 Dimethylol urea lbs 25 Polyvinyl alcohol lbs 25 aooi ns hes ngred en s e he to 1 and the pI-I adjusted to about 4.0 with paper maker s alum. The mixture is agitated about thirty min: utes and then diluted with water to a volume of p roximate 100 ga o s n the p a ain e J'llsted to 5.5-6.0 by the addition of an alkali. This mixture is applied at the calender stacks at a rate that will consume approximately 3.0 pounds of solids of the starch resin composition nd 1.6. ounds o o v nyl. oh l e on of treated stock. This treatment imparts greatly increased resistance to abrasion under both wet and d e nd t e e and en m o m n n 015- ture resistance to the treated layers of the board, whil the pr ncip un t on. o he l v n e cohol is to improve the printability of the outer surface and increase its grease and soiling resistance. The quantity of solution per ton of board treated may be varied within reasonable limits; I have found that the amount specified above gives satisfactory results; and any substantial reduction in the quantities reduces the eifectiveness of the treatment, while increased quantities are unnecessary for the proper functioning of the board for the purposes intended.

Step 4..+The filler sheets are prepared on the cylinder machine in the conventional manner with kraft pulp derived from long, stron fibered wood, carefully digested and refined for obtaining maximum strength properties, with a furnish controlled to meet the required test specifications. The filler is a 90 pound sheet, caliper .025, testing 110 pounds per square inch. It is sized with not less than 75 gallons of a rosin or wax size or a combination of sizes to insure an average absorption number of the sheet of not more than 350.

Step 5.-A 4-ply solid fibre board is made on the conventional laminating machine or paster by gluing two filler sheets with a front and back liner with a liquid adhesive composition which forms a water insoluble irreversible gel upon setting. An adhesive composition entirely satisfactory for this purpose is described in pending application for Letters Patent, Serial #44,164, filed August '13, 1948, by J. J. Koenig et al., now Patent No. 2,597,006. This adhesive composition is essentially a soya protein base glue dispersed in an aqueous medium with potassium hydroxide or other dispersing agents.

Other water insoluble adhesives may be used in forming the combined board, such as poly.- vinyl alcohol compositions and the well known starch urea glues, but I have found that the protein base adhesive is more satisfactory, both from cost and operating standpoints. Accordingly my preferred practice is to prepare the adhesive for use on the laminating machine in the l w n manner Sftep 1.--Six hundred and sixty-five (665) galions of water are run into amixing tank equipped with efficient agitation and means for tempera: ture control. The water is brought to a temperature preferably of about 80 F. While the temperature of the, water may be varied within reasonable limits, for example, between 70 F. and not exceeding 100 F., cooler water tends to delay the dispersion of the proteins, and-water of higher temperatures accelerates hydrolysis oi the protei c n and shou be a o Step 2.--Agitation is maintained throughout the p ep n o he adhe v o o i since, as ingredients are added, a thixotropic suspension is formed, whichrequires continued agitation to maintain uniform consistency.

-Qn a on. of s am d st ed n .1 is added, which acts as wetting agent for the dry ingredients subsequently added and reduces the viscosity of the finished adhesive, thereby enhancing its spreading and flowing characteristics.

Step 4.--.-Eighteen hundred pounds (1800 lbs.) of Klondyke DRG clay are added.

Step 5.-Afte r the clay has been thoroughly mixed with the water, "42 pounds of sodium pentachlorophenate dissolved in 15 gallons 'of water are added. This material is a fungicide and preservative for protein and carbohydrates and is added at this stage because, being strongly alkaline, it aids in the dispersion of the clay par ticles and thickens the dispersion slightly. It is also an aid, due to its alkalinity, in peptiz'ing the ubsequen l added P o e n Step 6.?Add 1600 pounds of soya alpha proein, ef rabl o a i c i of 350 t .500 mm;- noises;-

ten t h addit n of the e nh P tein, agitation should be maintained for minutes to insure thorough wetting and dispersion of th nr tem ar i es.-

Step 8.-.-One hundred and twenty-eight pounds .2. l s of p tass um. h drox d s ed in. 59 a n f wa r. re adde s a y s ss le upon the completion of the mixing of the protein and clay. The mixture will be observed to thicken immediately after the addition of the t si m h ro de. nd continues t thie en until peptization is complete. During this step in the process, the protein particles swell into translucent globules and finally rupture. The clay particles likewise apparently break down and form colloidal combinations with the protein and potassium hydroxide, since no clay particles can be discovered when a thin film of the finished composition is examined under a microscope at 100 diameters magnification. Distinct advan: tages result from the addition of the clay in advance of the proteins. This practice insures a maximum dispersion of the clay and avoids any tendency to form lumps, such as occur when the clay is added simultaneously with the protein or subsequent to the protein. In addition, it is believed that the clay particles act as an aid to the complete dispersion of the protein by a grinding action on the. surface of the protein particles, thus exposing more and more protein surface to the action ofthe subsequently added alkali solution.

Step 9.Peptization of the protein is completed inthirty minutes after the addition of the alkali solution. A suflicient amount of water is then added tobring the. volume to exactly 1056 gallons durin continuous agitation. The temperature throughout the preparation of the mixture is controlled to between 70 and 100 F. Upon completion of the batch, the temperature is adjusted to between and F., and is then ready for use. Because of the thixotropic nature of the adhesive, it should be maintained in motion at all times, including storage, by mild agitation.

This adhesive Solution is applied on the laminating-qmachine to the component liner and filler sheets at the rate of approximately one gallon or less per M square feet of glue line, or three allons per M square feet of the consolidated 4- pl b ers e ombine boa hu P e ared will showno ply separation whatsoever after being subjected to the Armyand Navy JAN.P-.-.'108 test. which provides for immersion in water at 75 for t nt fonr h r The board has a minimum Mullen test of 550 pounds per square inch, and not less than 300 pounds per square inch after twenty-four hours immersion in water according to the JAN-P408 specifications. It has a puncture test in its dry state, measured according to the G. E. standard method, of at least 550 ounces per inch of tear, and after immersion in water of 450 ounces per inch of tear.

The greatly increased resistance to abrasion and soiling is illustrated by the test of the typical commercially available multiple trip bottle carrier fabricated of solid fibreboard coated with paraffin. The test was made by placing three of the typical paraffin coated containers and three containers of the same dimensions made of fibreboard produced according to the process of my invention in the standard revolving drums, described in TAPPI standard T 800 sml l.

The lids on both types of containers were closed and sealed. A greasy, sweeping compound, together with floor sweepings were introduced into the drum, thus both types of boxes were exposed to the same wear and soiling conditions. The drum was revolved 12,870 times at the rate of 3 or 4 R. P. M.

At the conclusion of the test two of the standard paraflin coated boxes fell completely fiat, the vertical corners having worn through completely. The third paraflin box was in almost as dilapidated a condition, the sides barely hanging on. All three of the old style boxes were unfiit for any further use.

The boxes fabricated from'the fibreboard of my invention, after the 12,870 revolutions of the drum were still within about 80% of their original condition. They had sustained scuffed edges and. slightly rounded corners, but all were still in good serviceablecondition.

The standard paraffin boxes were badly soiled with dirt and filth adhering to the surfaces, even though practically all of the paraffin wax had penetrated into the board. All corners and edges were badly scuffed and dirt had been picked up by the loose fibers. All three of the boxes were soiled and scuffed beyond any further use.

The boxes fabricated from the fibreboard of my invention showed some slight soiling at the corners and edges where the fibers had been ruffed up. able condition and of far better appearance than the standard paraffin coated containers.

Another physical factor which is important in solid fibreboard for the purposes described is the sliding resistance. This condition of the surface of a combined board is usually expressed as a coeflicient of friction determined by the method hereinafter described. A low coefficient of friction results in cases due to slippage of stacked sheets and the containers fabricated therefrom, L

while a high coefficient of friction increases the labor of handling both the sheets and the containers made therefrom. The combined board of my invention has a coefficient of friction which has been found quite satisfactory in practice, between 250-350.

The board is eminently satisfactory for fabricating multiple trip carriers capable of twentyfive or more loaded trips under the most severe transportation and weathering conditions.

The linerboard prepared by the process of my invention at the end of Step 4 of the foregoing example of my process, is suitable and may be used to advantage for purposes other than forming the laminated board described in the All three boxes were still in a highly use- Mullen or bursting strength TAPPI official standard test T-403 m-45.

Puncture test TAPPI tentative T-803 m-44.

Water immersion test The joint Army and Navy specification JAN-P- 108, entitled Packaging and Packing for Overseas Shipment by Boxes, Fibreboard (V-board W -board) Exterior and Interior.

The conditions of immersion are described on pages 6 and 7 of the specification under paragraph headings:

Sliding test, expressed as coeflicient of friction This test is made according to the following procedure:

Obiect.The object of this testis to measure the resistance of a coated surface to slipping or sliding.

Apparatus-A variable inclined plane.-This consists of a 13" x 13" board pivoted at one'end to a base. The loose end of the board is provided with means for raising it at a constant speed of 8" per minute. A vertical scale (inches by sixteenths) is attached to the base 5 from the pivot point.

Procedure.-The variable inclined plane is placed on its lowest position. A 12" x 12" sample of the coated material is attached (coated side up) to the-movable plane so that the direction of slide when the angle of the plans is increased will be along the machine or fibre direction of the material. Another 12" x 6" sample is folded around a 12# iron weight in such a way that a 6" x 6" coated area is fiat under the weight. This weighted sample is then placed on the sample attached to the movable plane so that the fibre directions are parallel and the coated faces are together. The mechanism for increasing the angle ofinclination is started. As the inclination increases the scale reading at the level of the moving board is watched, and at the instand the Weighted sample begins to slide over the stationary sample, the scale is read to the nearest sixteenth of an inch.

Good averages may be obtained by testing three sets of samples of the same materials five times per set and taking a grand average.-

The average reading thus obtained is an index of how the material resists sliding, which is an important factor in the trucking and stacking operations.

It is only necessary to measure the vertical a 1-1 risebecause it is directly proportional to the 'co= eincient of friction. I From thedata derived bythe procedura the coe'flieien't of friction is calculated by the well known methods.

Absorption number This test is made by the following method, which is well known and generally recognized in the paperboard industry.

6" x 6" samples of the components to be .tested are immersed vertically in water at 75 F., for ten minutes, after which the samples are removed from the water, the excess surface water is removed by blotting, and the weight gained during the immersion is calculated. This Weight gain expressed in centigrams is known as the absorption number.

WhatI claim is: i v, h u

, A composite u antie us a a r d .L i wet strength solid fiberboard consisting of permanently adhered to ether opposed outer liner sheets with a substantially co-extensive filler sheet therebetween, a water resisting jrosins'ize substantially uniformly distributed throughout all of said sheets, and, in part, serving to retard water penetrating the edges of the solid fiberboard by capillary attraction, the liner sheets being composed of at least 'three plies, a water insoluble adhesive permanently securing the inner-most ply of each liner sheet throughout their entire area to the adjacent side face of the filler sheet, and a water and abrasion resisting resin substantially uniformly distributed, along with the rosin, only throughout each of the outermost plies of the liners, thus supplementing the bonding of said pliesandserving to Ldoubly retard iwater penetrating the exposed surfaces of the liners.

2. ,5 composite substantially stable, rigid, high wet strength solid fiberboard consisting 'of per- 1in enny adhered together opposed outer liner s with a substantially co-exte nsive filler :she'et therebetween, a water resisting rosin size inan amount tolinsure, an average absorption number of about 350 substantially uniformly distributed throughout all of saidsheets, and, in part, serving to retard Water penetrating the :edges of the solid fiberboardbycapillary attraction, theliner sheets being composed of at least three plies, a water insoluble adhesive perma- In ntlysecuring the inner-most'ply of'each liner sheet throughout their entire area to the adjacent side face of the filler sheet, and a water and abrasion resisting resin; substantially unif rml i r but al ih nrgs nijon y th ou h u h o ot r e -P ie 9 th iin'els, and 'intheratio of 1% to by weight with respect to the treated liner plies, thus supplementing the bonding of saidplies and serving to doubly retard water penetrating 'the ex- "posed surfaces of the liners.

an composite substantially stable, rigid, high 'wet' strength solid fiberboard 6f not less thanfsoet 'oiits 'dry bursting strength csnsisun 'ofpema- 'nently adhered together opposed outer liner sheets with two substantially co-extensive filler sheets therebetween, a water resisting rosinsize in an amountt'o insure an averagefabsorption number of about 350 substantially uniformly distributed throughout an or said sheets, and, in part, serving to retard water penetrating the-edges of the solid fiberboard by capillary attraction,

the in r. sh ts b n p s at a le 'tf 'h plies, a water insoluble adhesive perman'entlyse- 12 in eia ia a e th fi l fr sl etsjend the inner-in'ost'ply of each li ner sheet throughout their entire area to theadjacent side face 'ot the filler sheet and a water and abrasion resistin resin substantially uniformly distributed, along with the rosin, only throughout ea'ch oithe outermost plies of the liners, and in the ratio of l 7 to 5% by weight with respect to the treated liner P ie t su plem n i afim .tb 'ii'iis s pl e a d ervin ..id.b b r t r Wa r ene. e. xro seriee s wel ee i t.

I 4'. The process of makinga composite substant a' lr b e rigid, i We? Str n th. s be bo d cd 'ris nsmi i 's ei rl n x s p n te t r e rm ned amb s bi. ll ilej i fibrous "material and rosinsize to form a slurry, with the rosin si'ze 'unifo rmly distributed therein, providing separate sources of the slurry, introducing a water and abrasion resisting resin into one source of the slurry, simultaneously forming and uniting individual outer plies 'o'f fibrous material from said'one'souroe, and forming and unitingan inner ply from another source containing only the fibrou material and rosin, uniting all of the said plies to form liner sheets, forming a filler sheet from the slurry containing only the fibrous'lnaterial androsin, disposing the filler sheet between opposing inner plies of two liner sheets, and permanently joiningthe said sheets together with a water insolubleadhesi ve. v '5. The process of making a composite substantially stable, 1'igid,'high Wet strength, solid fiberboard comprising mixing a preponderance of 'wa te with predetermined amounts of cellulosic fibrous materiarandro'sin size to form a slurry, with the rosin size in an amount to insure an average absorption number of aboutEbOuniformly distributed therein, providing separate souro'es of the slurry, introducing a water and abrasion resisting resin in the ratio of 1% to 5% by weight with respect to the treated liner plies into one source oi theslurry, simultaneously forming and uniting individual outer plie fibrous'inaterial from said one source, and forming and uniting an inner'ply from another source containing only the fibrous materialand rosin, uniting all of th'e said plies to formliner sheets, forming a filler sheet from the slurry containing only the fibrous material and rosin, disposing the filler sheet betweenopposing inner plies of two liner sheets, and permanently joining the said sheets together with a water insoluble adhesive, r

6. The process of making a 'composite substantially stable, rigid, high Wet strength, 'soiid fiberboard of notless thanbi ib of its dry bursting strength comprising mixing a preponderance of water, with predetermined amounts of cellulo si c fibrous material and rosin size to form a slurry, withthe rosin size in an amount to insure an average absorption number of about 350 uniformly distributed therein, providing separate sources of the slurry, introducing a water and abrasion resisting resin in the ratio of 1% to'5% by weight with resp'ect to the treatedlinerplies into one source of the slurry, simultaneously 13 I most ply of each of the said liner sheets together with a water insoluble adhesive.

WILBUR F. GILLESPIE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Number Date 10 1,438,966 Perry Dec. 19, 1922 2,050,382 Rowbotham et a1. Aug. 11, 1936 2,271,620 Brier Feb. 3, 1942 2,322,887 Schwartz June 29, 1943 Number Name Date 2,352,293 Sherman June 27, 1944 2,385,714 La Piana Sept. 25, 1945 2,399,489 Landes Apr. 30, 1946 FOREIGN PATENTS Number Country Date 119,092 Australia Oct. 16, 1944 OTHER REFERENCES Industrial 81 Engineering Chemistry, July 1942, pages 817-820, Soybean Protein Adhesive Strength and Color, by A. K. Smith and Herbert J. Max.

Claims (1)

1. 4. THE PROCESS OF MAKING A COMPOSITE SUBSTANTIALLY STABLE, RIGID, HIGH WET STRENGTH, SOLID FIBERBOARD COMPRISING MIXING A PREPONDERANCE OF WATER, WITH PREDETERMINED AMOUNTS OF CELLULOSIC FIBROUS MATERIAL AND ROSIN SIZE TO FORM A SLURRY, WITH THE ROSIN SIZE UNIFORMLY DISTRIBUTED THEREIN, PROVIDING SEPARATE SOURCES OF THE SLURRY, INTRODUCING A WATER AND ABRASION RESISTING RESIN INTO ONE SOURCE OF THE SLURRY, SIMULTANEOUSLY FORMING AND UNITING INDIVIDUAL OUTER PLIES OF FIBROUS MATERIAL FROM SAID ONE SOURCE, AND FORMING AND UNITING AN INNER PLY FROM ANOTHER SOURCE CONTAINING ONLY THE FIBROUS MATERIAL AND ROSIN, UNITING ALL OF THE SAID PLIES TO FORM LINER SHEETS, FORMING A FILLER SHEET FROM THE SLURRY CONTAINING ONLY THE FIBROUS MATERIAL AND ROSIN, DISPOSING THE FILLER SHEET BETWEEN OPPOSING INNER PLIES OF TWO LINER SHEETS, AND PERMANENTLY JOINING THE SAID SHEETS TOGETHER WITH A WATER INSOLUBLE ADHESIVE.

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