US2643186A - Process of forming artificial board - Google Patents

Description

Patented June 23, 1953 PROCESS OF FORMING ARTIFICIAL BOARD Gordon E. Tower, Corvallis, reg., assign or to Chapman Forest Utilization, Inc., Corvallis, 0reg., a corporation of Oregon No Drawing. Application April 10, 1948, Serial No. 20,353

2 Claims.

My present invention relates to the fibreboard art in that the principal object of the present invention is to provide a novel method for forming a novel fibreboard, the invention, however, being applicable to the formationof other fibre products having boardlike characteristics, such as molded panels, plates, insulating members and other articles of a similar nature.

The principal object of the present invention is to provide a board which will have increased strength, modulus of rupture, resistance to moisture absorption, resistance to swelling or warping, and resistance to the effects of acids, alkalies, steam, heat, dry rot and fungus or to destruction by termites and rodents.

It is Well known in the art that boards or boardlike products may be created by reducing wood or woody substances such as cornstalks, straw, leaves, grass, hemp, esparto grass, flax, papyrus, ramie and other fibrous substances to fibres, forming a water slurry of the fibres, adding thereto a solution of a phenol-formaldehyde resin, straining the water from the fibres to form a mat, and compressing the fibre mats While heating them to convert the resin and the natural lignins or other resinous substances present in and among the fibres, to an infusible, insoluble state. Examples of such processes are disclosed, for example, in the patents to Baekeland 1,160,362 and 1,160,365, Cheetham 1,776,885 and Novotny et a1. 1,616,062. Various means are known for disintegrating wood or woody substances into fibres such as by grinding or abrading chips of wood, by soaking wood chips in water, or subjecting them to steam, until they disintegrate into fibrous bundles, by chemical digestion, or by the well known explosion process disclosed in the patent to Mason 1.578,609. Various means are known whereby fibre slurries may be made into boards, such as wholly or partially disclosed in the patents to Mason 1,603,503, 1,603,504, 1,603,505 and 1,603,506; Vogt 1,718,011; Vogt et al. 1,718,012; Streeter 1,763,910; and Mason 1,767,539. It is the collective teaching of the art as identified above that a board or boardlike article having a density ranging from 0.5 to 1.0 or higher and composed of fibres bound by C-stage phenolic resins or the natural resins of the wood fibres, or by both, may be formed. In the process of consolidating the boards or other articles wet mats of fibres are preferably heated between rolls or platens at temperatures higher than the boiling point of water and pressures of at least several times atmospheric pressure for various periods of time and with various alterations of the tem- 2 perature or pressure during the time the articles are being pressed. During the drying operation the water which is present in the wet mat of fibres is either squeezed from the article as freely running hot water or escapes therefrom as steam. An object of several of the foregoing patents is to provide ways and means whereby migration of the resin either to or from the surfaces of the sheets, and migration of other substances present in 01' among the fibres such as wood sugars which char upon contact with the hot platens, is diminished, An object of the present invention is to provide a method whereby the resin added to a fibre slurry is retained during the hot pressing operation in intimate contact with all of the fibre,

without migration thereof to surface or edge areas under the force of escaping steam and running hot water under pressure.

In the foregoing patents the step of adding a phenolic resin in comminuted state or in solution is disclosed, and the precipitation of the phenolic resin after thorough'mixture with the slurry is also disclosed. In accordance with my improvement a time lag is permitted between addition of the resin solution to the fibres and the precipitation thereof, such time lag being of sulficient length to establish a firm bond between the fibres and the resin molecules. The bond thus established appears to be partly in the nature of adsorption, a surface phenomenon whereby molecules of the resin attach themselves to the surfaces of the fibres, and absorption, an osmotic action wherein the molecules of the resin intermingle with the molecules of the fibres, perhaps accompanied by a chemical linkage of the phenolic material with the cellulosic substance forming the fibres, or with other natural substances found with wood fibres such as lignins and'hemicellulose.

Adsorption in itself takes place rapidly. However, it requires time to manipulate the resin molecules into position to be adsorbed due to the irregular surfaces of the fibres and the cell wall openings. If the time of mixing is short only those resin molecules which have had the opportunity to be adsorbed by the outside surfaces of the fibres, and particles physically held by the fibre Web, are retained, with the result that a large proportion of the precipitated resin is freely suspended in the water slurry and drains off from the fibres in the white water resulting from the screening process of forming a wet mat of tangled fibres. In accordance with my invention, I permit sufiicient time for the processes of difiusion, absorption and adsorption of the resin molecules to take place throughout the fibre slurry. Upon precipitation those molecules on the surface of the fibre act as nuclei about which resin particles form from resin in the water solution surrounding the fibres. Whatever the exact phenomena might be, I have discovered that permitting the resin to remain-in solution for a substantial period of time with the fibre particles, such as approximately one-half hour, 7 results in the retention of eighty to ninety per 10 cent of the resin by the fibres, whereas immediate I, precipitation results in retention of a lesser proportion, such as approximately fifty to sixty percent. a

The rate of difiusion into and hence the re tention of the resin by the wood fibres appearsto, be affected by the sizes of various openingsin the individual fibres such as pits, fibre cavities and cell wall capillaries, into which the resin diffuses.

While any of several phenolic resins may be utilized with good result in my process,- I have also determined that a resinpolymer 'of large molecular size is most desirable, apparently be-- caus the attraction or bond between thefibres and resin is most advantageous if the -resin molecules remain largely upon or close to. the surfaces or" the fibres. Some resins of smaller molecular siz penetrate deeply into the'interiors oi the fibres and thus failto bind adjacent fibres together when converted into C-stage. -I have determined that-many of thecommercially available phenolic resins maybe utilized to good advantage, but I prefer a phenol-formaldehyde resin, such resin being ofthetyp 'which iswatersoluble and alkaline in nature.- I prefento'f-orm an alkaline solution of awater-soluble phenolic condensation product in the-B-stageor in the incipient C-stage-as expressed.by Dr V-. Redfernof the AmericanMarietta-Chemical Company..40 In accordance with Redferns discoveriesthereaction of a-rnixture of phenol and formalde- A hyde may be advanced toform a resin almostto the end of the-B-stage-by thecontrolled stepwise addition of sodiumhydroXide-as a-catalystand solubilizer. .It is not mynintentionto relateherein the exact detail of Redfern s-process -it being sufficientto state thattheproductobtained from H his process is. an alkaline, water-soluble, phenolformaldehyde resin. in incipient C.-stage having a very-largemolecular. structure. This resinshasm the additional advantage of being-recapturable1... fromprecipitation a. number/of times .Thatcis, 1 after the alkaline solutionhasbeen precipitated. the resin may be reusedby. restoring its alkalinity. a number of times,.whereas asomeresinuproducts which havebeenbnce precipitated.form .an end. product, all of which cannotbe returnedtosolm... tion by alkalinizing the water holding the pre-H... cipitate. It is immaterial to. the. present.inven-. l. tion to describe the-methodof manufacturing Redfernfs resin, such method .beingdisclosedand claimed in the copending ,applicationof D. V. Redfern, Serial No. 722,016, filed September; 3, 1947, now ReissuePatent 23,347, reissued..March, 20, 1951. Such a resin is hereinreferredto as. an intermediate condensation product. of the phenol-formaldehyde type in incipient, Q-stage resulting from controlled stepreactionshin the presence. of an alkaline catalyst such as sodium hydroxide.

I have discovered that delayed addition of acid. 0r acidic. salts .to acidify or substantially neutralize the alkaline. mixtureof fibresandresin in aslurry ,to establish, retentionof.theresinby article.

the fibres accomplishes results comparable to results which have heretofor only been achieved by hydrolizing or otherwise treating cellulosic fibres until the fibre has been converted to viscose or a purified cellulose as distinguished from a ligno-cellulose type of material. The hydro- 1i2ing a.cti0nc0nvrts rawtwood fibre, as distinguished from chemically produced fibres, apparently both chemically and mechanically, to a slimy, viscous substance having the individual fibresm ore or less; reduced to a pulpy or gelatinous state, each fibre having far less mechanical strength than theoriginal fibre. By my process I amable to achieve firmly bonded fibrous products in which the individual fibres remain as naturallycreated with the exception of some swellingdue to absorption of water. This is accomplished without expensive machinery such as beatersand jordans, and without the loss of time required for producing hydrolized cellulose. In my process I am able to take-grecn-or dry-wood mechanicallyconvertit to individual fibres-or I 1 smallbundles offibres-by grindingror crushing: machines or by mechanical defiberizers havingateeth-which gouge-slivers-from the leng-th of I 1 wood stock, Or othersuitableprocess, and form a slurry thereofawhich may be immediately started through the 'board forming process.--No digestion or other chemical: reaction is Irequired butdigested pulp maybe used ifdesired.

The slurryof fibres. is v.formed by. adding water/r. preferably including [white water. drained -from previouslyformed mats or resin-bearing fibresso as to recapture the .particles of. precipitated resin.v which have escaped -from.thei fibres ofthe-pre-.... viously. formed. ..mats,, such precipitated; .resins being mechanically retainedby the. strainingw... action of the fibresbeingformed into-mats, or redissolved. when an alkaline solution of resinds added to the .s1urry... .This vredissolving..rof the resin is more readily accomplished.- and. may .be repeatedanumber of timesvwitha resin suchas formed. by the .Redfern.. process, but other... phenolic resins. may .be utilized with. some ,degree of success since..therprecipitate..which,will. not.,.l redissolve, is,v largelyl-recaptured by the. straining: actionof the fibres,.- espeoialy...when,.the. fibres. have become somewhat: stickytdue to the adher-a. encethereto of resin sin accordancev ,with my process of fibresby separating them into indivi u l fib e bi fibre; bundles of small-,dimen sions.From the; h r finers he lurry is ump d i cza pr ip ta in v pr f y hav n a ta ine m nath re nlt assure thorough ,mixing of the; resin; solution; W c is added at. t i p n -v.1 fl e n-.sol ic. is p fe l ad edas an al al es utiQn...t 1H. ou t of resin be nesva ied in ac ordanc with. the hardness ,or strengthlor others-qualities;de-,,, siredin: the finished product. Resinin the pro; t

portionof two percent resin solidsto fibre based.v on the dry weightof thefibre willgivea 531111531 factory hardboard .suitable .ior 'many purposes... while as high'as. forty percent/resin may-be in.- corporated to -form: a non-.porous. boardl or w The amount of. resin can be adjustedto. give properties tothe product in. accordance. with c the intended use. of the; finishedproduct, buts, threev and one-half percentis-a suitable-amount. .4

. for .most purposes.

-.,The;resin is. allowedtopremaininsolution. for a .l

sufficient period of time to establish sorption thereof. By the word sorption I mean to include the phenomena of adsorption, absorption and diffusion. Although some of the resin is immediately retained, I have found that approximately one-half hour is required as the minimum time for the retention of over ninety per cent of the resin. The amount of retention may be expressed against the time factor as a parabolic curve, for example, less than fifty per cent being retained. in the first five minutes, about seventyfive per cent in the first twenty minutes and about ninety per cent being retained in thirty minutes. If the resin remains in solution for a longer length of time the curve flattens out toward infinity with the additional advantage gained in several hours time being slight. The practical application of my process therefore comprises the step of allowing the resin to remain in solution in the range of twenty minutes to one hour. After 'sorption of the resin is accomplished, precipitation of the resin is achieved by acidifying or substantially neutralizing the alkaline mixture. Sulfuric acid, hydrochloric acid or acidic salts such as alum may be used, but for reasons of economy a ten per cent solution of sulfuric acid appears best. The pH of the fibre resin slurry may be between 7.5 and 10.5, and sufiicient acid or acidic salt is used to achieve a final pH of about 5.5. The final pH is not critical and may be in the range of 4.5 to 6.0. Immediately upon establishing thorough mixing of the acidifying agent the slurry may be strained to form a wet mat of entangled fibres having the resin bound thereto, at least partially by sorption, which may then be consolidated under heat and pressure to form the desired end product. By varying the temperature and pressure, as well as the thickness of the article being formed, the density of the final product may be varied as desired. For example, boards may be formed with densities ranging from 0.5 to 1.4 in thicknesses of one-sixteenth to one inch or greater.

After the formation of the boards or other articles their humidity is adjusted by conditioning them for a sufficient period of time in a humid atmosphere until they reach a moisture content of approximately seven per cent.

Boards made in accordance with my process have improved charateristics, such as the modulus of rupture in static bending being 6500 p. s. i. for four per cent resin to dry weight of fibre when using Redfern resin, and 5100 p. s. i. to 5800 p. s. i. when using several other phenolic resins, as compared with 2800 p. s. i. for a board incorporating no artificial resin. Samples immersed in water for eight days at 70 F. will swell in thickness approximately thirty per cent when incorporating four per cent of any of the resins as compared with approximately seventy-five per cent for a board having no resin; and will swell laterally approximately 0.15 per cent when incorporating four per cent resin as compared to approximately 0.7 per cent for a board having no resin. The above figures were taken from samples of board formed in identical manner in all cases except for the resin variation. The boards measured approximately 0.21 inch in thickness and had a specific gravity of approximately 0.95.

In a variation of my process, in addition to the addition of resin as expressed above, I add about 0.5 per cent of a paraffin size, the percentage being by weight of solids to dry weight of fibres. This paramn size is added simultaneously with the addition of the resin, preferably as an emulsion. The pH of the slurry after the addition of the resin and size is usually approximately 9.5 to 9.8. The precipitation of the resin is preferably carried out by adding a ten per cent sulfuric acid solution until a pH of 6.0 to 6.5 is reached, then adding a ten per cent alum solution until a final pH of 5.0 to 5.5 is reached, after which the board may be immediately formed. The acidification could be entirely accomplished by the use of an acid alone or an acidic salt alone, but again economy and ease of handling dictates the use of a large percentage of sulfuric acid and a final adjustment of the pH by the use of alum. Thus when the board is formed the paraffin is intimately associated throughout and aids in repelling moisture and water.

In referring to the resin as a phenolic resin I do not necessarily mean that a phenol-formal dehyde condensation product should be utilized, since various other phenols such as cresylic acid and resorcinal may be substituted for the phenol and various other aldehydes may be substituted for the formaldehyde, as is well known in the art. In referring to the condensation product as being in the B-stage or incipient C-stage, reference is made to the classification established by L. H. Baekeland in his article The syntheses, constitution and uses of Bakelite, published in the Journal of Industrial and Engineering Chemistry, volume I, Number 3, March 1909, pages 149, 155,

' in which he defines three stages of phenolic resins as follows: The A-stage or initial condensation product may be liquid, viscous, pasty or solid at ordinary temperatures. It is soluble in alcohol, acetone, phenol, glycerin and similar solvents and in sodium hydroxide. Solid A is brittle and melts if heated. All variations of A heated long enough under suitable conditions will change first into B, then finally into C. B-stage, or intermediate condensation product, is solid at all temperatures. It is brittle, being slightly harder than solid A at ordinary temperatures. It is insoluble in all solvents but may swell in acetone, phenol or terpenol without entering into complete solution. When heated it does not melt, but softens and becomes elastic and rubberlike, but upon cooling again becomes hard and brittle. Further heating under suitable conditions changes it into 0. Although B is infusible, it can be molded under pressure in the presence of heat to a homogeneous, coherent mass and further changed into C by the proper application of heat. C-stage or final condensation product is infusible, insoluble in all solvents, unattached by acetone, indifferent to ordinary acids or alkaline solutions, is destroyed by boiling in concentrated sulfuric acid, but stands boiling with diluted sulfuric acid, does not soften to any serious extent if heated, stands temperatures of 300 C., and begins to be destroyed by higher temperatures and chars without entering into fusion.

I have found that any of several water-soluble, alkaline, phenolic resins in the intermediate condensation product stage, which may be purchased in open market, may be utilized to advantage in my process, such resins being in the B-stage in solution in an alkali such as sodium hydroxide, even though Baekelands classification seems to deny solubility. I prefer the Redfern resin for its greater retention, the improved results ther from, and its ease of handling and recapture, which resin Redfern describes as being in the incipient C-stage, meaning that he has produced a resin at the extreme limit of the B-stage which may rapidly convert to C-stage resin upon the pp i ati r e t- W en u n any. 1 8111 933:

resin in B stagel find-thatthe-retentlon thereof achieved inmyprocess issuchthat theresin and Y other chemicals presentin the fibres remain -jn place when heat and pressure are applied to a wet mat so that the finalproduct is homogeneous o ho t a d is n u f ce-d colo dp,0

charred'by thepresence of burnt sugals or the like. The homogeneity of the" final product is more pronounced with the use of Redfer-rrresin,

since the conversion of the resin intothefinal infusible, insoluble C-stageproduct is more rapid-- 1y achieved after the application of heat; and pressure is begun. The Redfern resin is sold as American-Marietta 113, and other usable-resins;

are Adhesive Products 3910, --Durez ;1-l 857 and Bakelite BV 9700..

Having described the invention in particularity andin its broader aspects, Lclaim as my inventionall such modifications thereof as maycome within the true spirit and scope of the appended claims.

I claim:

1. The process of. forming artificial boards and boardlike articles which comprises reducingcellu losicmaterial to fibres, mixingthe-,fibreswith water to form a slurry, thoroughl mixing into, i.

the slurry an alkaline solution'of a water-solublethermosetting, intermediate condensation prodnot of a phenol-aldehyde resin in the proportion of about 3.5 per cent resin solids to fibres and.

about 0.5 per cent paraifin size based-on the dry 1 weight of the fibres, agitating the mixture for at least one-half hour, adding an acid in suificient, quantity substantially to neutralize the mixture in order to precipitate the resin in situ and simultaneously adding sufficient alum to coalesce the sizeand fibres, straining the waterirom the slurry .to form a mat of entangled, resin-bearing,

sized fibres, and compressing the mat while-heat ing it to formv a finished product of sized fibres;

at least partially bound together by the infusible,

to form a mat of entangled, resin-bearing, ,sized fibres,- and compressing the mat while heating it I to form a finished product of, sized ,fibres at. least}. partiallybound by an infusible, ns0lub1e, final condensation product of theresin. Y,

GORDON'E; TOWER? References Cited in theflfileqf, th 1p UNITED STATES Number Name Date-- Re.'23,347 Redf ern -s; Mar: 20, 1951 1,160,365 Baekeland Nov. 16, 1915 1,684,755- C1app' Sept. 18,1928 2,027,090 Carter Jan. '7; 1936 2,036,156 Lundback; Mars-31, 1936 2,068,926 Nevins; Jan-26, 19 37 2,173,391 1 Ellis; Sept.-19, 1939 2,343,090 Smith- Feb; 29, 1944 2,539,183 Child Jan. 23, 1951- FOREIGN PATENTS Number Country Date.

28,155 1:. Great Britain,- June 29, 1911 OTHER REFERENCES Boehm: Paper Trade J pp. -33, May2, 1 940,.

Claims (1)

1. THE PROCESS OF FORMING ARTIFICIAL BOARDS AND BOARDLIKE ARTICLES WHICH COMRPISES REDUCING CELLULOSIC MATERIAL TO FIBRES, MIXING THE FIBRES WITH WATER TO FORM A SLURRY, THOROUGHLY MIXING INTO THE SLURRY AN ALKALINE SOLUTION OF A WATER-SOLUBLE, THERMOSETTING, INTERMEDIATE CONDENSATION PRODUCT OF A PHENOL-ALDEHYDE RESIN IN THE PROPORTION OF ABOUT 3.5 PER CENT RESIN SOLIDS TO FIBERS AND ABOUT 0.5 PER CENT PARAFFIN SIZE BASED ON THE DRY WEIGHT OF THE FIBERS, AGITATING THE MIXTURE FOR AT LEAST ONE-HALF HOUR, ADDING AN ACID IN SUFFICIENT QUANTITY SUBSTANTIALLY TO NEUTRALIZE THE MIXTURE IN ORDER TO PRECIPITATE THE RESIN IN SITU AND SIMULTANEOUSLY ADDING SUFFICIENT ALUM TO COALESCE THE SIZE AND FIBERS, STRAINING THE WATER FROM THE SLURRY TO FORM A MAT OF ENTANGLED, RESIN-BEARING, SIZED FIBERS, AND COMPRESSING THE MAT WHILE HEATING IT TO FORM A FINISHED PRODUCT OF SIZED FIBRES AT LEAST PARTIALLY BOUND TOGETHER BY THE INFUSIBLE, INSOLUBLE, FINAL CONDENSATION PRODUCT OF THE RESIN.