US2918398A - Artificial board - Google Patents

Description

Dec. 22, 1959 R. M. DORLAND ET AL ARTIFICIAL BOARD Filed July 6, 1955 lil Imam/m5 2,918,398 o ARTIFICIAL BOARD Rodger Malone Dorlandand `Maxwell Menuhn Yan,

Sault Ste.` Marie, Ontario, and Elliott G. Heslop, Sturgeon ]5`alls,0ntario,` Canada, assignors, by mesne as-V signments, to Abitibi Corporation, Alpena, Mich., a corporation ofDelaware .t t

` Application July `6, 195s, serial No. $20,319 Claims priority, applicationlCanada February 19, 1953 ls) claims. (c1.` 16a- 132) This inventionrelates to afprocess `for making artificial board and to the product` of such process. ,A

This application is a continuation-impart of application Serial No. 362,654, filed .lune 18, `1953, now abandoned. `It is well known that anartifcial board of-the type `known, as .hardboardgcanbe produced byta process includingthe debration and refining ofitiibrous material t t `such as wood` chips, followed by forming and dewatering Vof the wet lap on a Fourdrinier machine and consolida-.

`tion under heat and pressure toprovide a `hard compact fibrous massbound together bythe hemicellu1oses,tlignins and other naturalfbinding,constituents-of.the`wood. vIf

desired, additional ingredients can be added, such as sizes, for example, various waxes,land additional binding mate- Arials such as synthetic resins, for example, phenol- `formaldehyde resin. Y

A board produced in the foregoingmanner has certain disadvantages in relation to modern demands. The bers cause minute pits inthe surface, thus increasinglthe number ofcoats ofpaintrequired to achievea good` paint surface. In addition, the smooth surface of the'board has va dark appearance andis `frequently marked withdense kspotswhich` makes `it `ditiicult to achieve a blond Vfinish. ,The smooth surface of the board refers tothe surface :in direct contact vaithwthe vflat platens of the pressaduring ,final consolidation., The Arough surface is.,mprinted .with supporting wire screen `during the` consolidation.` For `zmost purposes the` surface appearance faceonly isV of importance.` i t, n The requirement for an improved surface hasbecome lof increased importance in recentyears.` Rising: wood ,.costsand changing economics have maderit necessary to usea `higher.proportionlofwaste wood-than formerly, :more of `the`brasher` and `lesssuitable-species` and even .,bark, 'and,have* made `it essential to increase machine speedstand therefore-,the vratcof water removal to;as Ahigh a point as possible. Coarser fibers of freer drainage of this smoothsurr 2,918,398 `Parented Dec. 22, 1959 ,wetlap. The top layerof better liber covers the poor fberstand bark specks and gives a board ofimproved appearance and surface qualities. VThis overlay process has serious limitations because the addition of relatively flarrgew,volumes` o f wateris necessary to make the secondary overlay stock flow and form properly. The water is difficult to remove, "Special equipment is needed to provide the slush stock. Also the secondary stock tends to ,fill fvalleysjin the underlying surface and w away from the peaks so that it is necessary to use a substantial .thickness of overlay to'give the desired evenness of surface. This `is costly. o o t t Yet another `solution which has previously been adopted is to laminate a thin board with good surface qualities to a consolidated base sheet formed from coarser bers. A sheet` of paperican beused as the surface laminate. This procedure has the disadvantage that a large amount Vof adhesive is necessary to give a goodbond between the base sheet and the surface sheet. `Even with a large amount of adhesive the `surface sheet may scale away under somel conditionse. 'Alsoa considerable quantity of additional equipment will be needed to" make a laminate lwhichwill in fact have an even surface. Inaccrdance with the present invention it is proposed 25 .tapply a sheet of paper to'the upper surface of the wet lap after `a large vproportion of `the w'ater has been removed from the wetlap but before the latter has been consolidated It hasbeen found that this produces an `irlterlocling of `the fibers -of theip'aper and of the wet lap and a bc'niiling` between the paper and. the wet lap due to the lignin's, Lhenicclluloses and other natural binding constituents 'of the pul`p Thus' thereis produced a board which has' the"gr`eatly`impr'oved surface qualities due to rthe fine `fibers lof` the paper, in which there is an integral bondi'gbetween the paper and the underlying coarser fibers'andwhich isof low cost as a thin surface layer is .used andas littlemodiiication kof the basic process is necessary. M lf f f A dry sheet of paper shouldibe used to give increased absorbency to the bindingconstituents of the wet lap.

o Additional strengthening of the `bond between the paper andthe 'underlying masscan' bei'o'btained bythe use of a thin layer of 'additional binder, although this invention considered in its broadest aspect isnot limited to the inclusinof such a binder; The binder tends to give a 'r'rioreunifor'm bonding b y` filling in and providing a bond v;therevalleys` occurfiin the base sheet. o Y

Particularly good results have `been obtained by using t "ardrying oil as abinder. Itfhas been found that,. in addihave been usedto, conform-,with the increasedmachine fspeeds andto ,offset the decreasein drainage` rates pro- .luced by bark particles. Bark, particles also result ina darkcrsurface.` f Thus a demand for an improved surface ,has, actually` coincided with -a deterioration `in surface lappeafallc- ,t :y .int yQne approach to, enhancing thesurface` appearanceu of `the smooth surJface; of theboard ewould'be touiseiner l fyyhic'h'ase'cohdary head bqx `l`y`` of specially prepared liuc fibers in a water suspension onto the partially f'rr'x'l'd ,1 HQWsYeft; this wuld, :Substantially increase :the s vtion tofthe contribution Vofthe drying oil to the bonding Vo'f "the paper sheet todthe `base `mat, the drying oil gives surface properties comparable to those of the treated board`prc' duced`by dipping or roller application of a drying `oil"to thc surface of the board, but with the` expendiftueofta farsmaller amount ofdryinfgoil. Part of the dryingoilalso gives ariwatfer resistant screen adjacent to `the surface of the paper to prevent the formation of water 'spots' whichfmight othervi/'ise be formed` during thehot lpressingsteptj These wat'erspotsare'believed to be due `torliquid water and-the solublestherein being forced to vthe "surfacefnd the water liashinginto steamon-contact `withthe lhot platen. "The water solublesugars-and other substances cause discolouration.` It has also been found thatlthe oils give a pleasant translucent appearance to the surface of the board, but that in spite of this translu- Vcency dense" spots on the surface of the base sheet are hidden. t

The sheet of paper used as an overlay in accordance with4 4thifsinvention may vary widely in grade, thickness andother qualities.. Preferably a low` cost paper of good absorbency such as news print is used.` Other suitable papers include sulphite, sulphate and neutralV `siilphite ywill have alreadytaken place.

semi-'chemical sheets. The weight of the standard newsprint sheet which is preferred is about 11 lbs./ 1000 sq. ft.

The binder can be a drying oil such as linseed oil or a composition consisting of a blend of drying oils with petroleum polymers. Other drying oils in addition `to linseed oil include soybean oil, tall oil and tung oil. Alternatively many other binders may be used including suitable formulations of synthetic resins such as phenolic resins, urea-formaldehyde resins and vinyl resins. Rubber latices such as butadiene-styrene latex and animal or vegetable glue or other binders also may be used. Ideally the binder should be cheap and effective in small amounts and should give a bond resistant to water, weather and heat. The binder should not stain the overlay. The quantity to be used will vary with thenature of the binder and other factors but in general a considerably lesser amount Will bev used than in the case of an ordinary laminate as the binder is not used as the primary bonding agent but only as an adjunct to the bonding obtained by the interlocking of fibers and use of the natural binding constituents of the base stock obtained in accordance with this invention. 11/2 lbs. of solids/ 1000 sq. ft. of board is the recommended quantity in the case of linseed oil. The quantity used will generally be within the range` of 1 to 5 lbs., but could be within the range of 0.5 to l0 lbs. The use of more than 2 lbs. does not significantly improve lthe adhesion of the paper to the base sheet, but more than 2 lbs. may be added to give a tougher surface. v1?/2 lbs. of phenolic resins and butadiene-styrene latex have also proved effective. Appropriate modifying agents, catalysts and driers may be added to the binder. Thus in the case of some drying oils, it may be desirable to add a drier such as a naphthenate of manganese, cobalt, lead or iron. In the case of linseed oil it has been found that where the oil is added prior to'consolidation the heat during pressing and subsequent ,baking sutiiciently hardens the oil.

The wet'v lap shoul'd'be fdewate'red to a consistency of 60 to 75% moisture content or aboutl solids before the sheet of paper is applied. To reach this consistency the water is reduced first by free drainage through the wires of the Fourdrinier machine, followed by suctionY drainage and the application of cold pressure rolls. The wet lap emerging from the pressure rolls will have a smooth surface which facilitates the bonding of the overlay sheet of paper. at this stage. In addition, most of the dewatering The overlay will therefore interfere. to la minimumextent with the dewatering of the pulp. The overlaysheet can be applied by rollers subsequent toV the cold pressure rolling and prior tojcorisolidation in the hotI press. `Where abinder .is to'be used it can be coated on the surface of the paper which willbe in 4contact with the wetlapprior to the applicationV of thepaper to the wet lapj. in the case of binders such as linseed oil and other drying oils it has been found that i the binder can alternatively be applied to the outerl'surface of the paper after'consolidation in thefhot press. The drying out in the hot press will makefther paper suf-- ficiently absorbent for-the binder t0 penetrate the paper overlay andthe'4 surface of the lbase sheet. ,When the board is baked the binder willfform a bond between the paperv and the -basel sheet. It is,lhowever, preferred that 'the binder be applied priorl toy consolidation undefrhe'at and pressure since va partaof the binder then formsa water resistant barrier to inhibit the formation of water spots."

In the drawings which illustrate the Vpreferred'embodiment lof this invention: 4

Figure lis a diagrammatic,'illustration of arnanner of Y carrying out the process of this invention.

Figure 2 is a vertical sectional View of aboard produced by theprocessof this invention. y r

The,V preferred embodiment o f this invention will be illustratedwith reference tothe production of l." hardboard with a newsprint overlay and using a linseed oil binder. Y

A furnish consisting of mixed hardwoods and softwoods in approximately equal proportions is providedby separate treatments of Wood chips in deiibrators A1 and A2 respectively and secondary refiners B1 and B2 and is passed into storage chests C1 andCz. with steam prior to and during the defibrator step. lThe consistency of the pulp entering the storage chests is about .4l/2%, by weight solids. The hardwood and softwood pulpsare combined in approximately equal amounts in mixing chest D where the consistency is adjusted to about 3%. Here suitable sizing materials such as a wax emulsion are added. The pulp is transferred through pipe E by pump F .to headbox G from whence it is fed onto the Wire screen of the Fourdrinier H. At this stagey the wet lap is about 3 thick. Part of the water is eliminated by free drainage in section I and further Water is removed by one or more suction boxes K and one or more sets of suction rollers L. The wet lap is then passed through one or more pairs of cold pressure rollers M. Preferably several such pairs of rollers are used with a nip pressure vaying fromlbs. per linear inch to 750 lbs. per linear inch. The wet lap sheet emerges about to l thick .and with a moisture content of about 65 and is translwith the paper overlay is consolidated under heat and pressure in'hot press S where it is subjected to pressure `varying between 50 and 650 p.s.i. at temperatures of about 390" F. during a pressing cycle of about 8 minutes total cycle. From thence the board is passed to baking oven T where it is treated at to 165 C. for about 3 hours or longer, after which it is humidiiied to about 7% moisture. i

,As illustrated'in Figure 2 the product is a basefsheet consistingl of a consolidated fibrous mass vU integrally bonded to overlay sheet V along lineW. There is an interlocking of fibers along line W which gives a firm bond. In addition, there is the combined bonding effect of the natural binders from the pulp and the drying oil. Partof the drying oil will be adjacentto line W and 'will be available for bonding. Part of the drying oil will be forced outwardly by the migration of binding constituents and moisture fromthe Wet lap to form a water resistant barrier shown as X. For the purpose of illustration barrier X is shown as being well defined. In practice it will not have clearly defined margins.

The product shown in Figure 2 has good abrasion resistance due tol the drying oil, a pleasing translucent appearance and superior bending properties giving small -v about one coatlof paint can be eliminated'by the irn- Aproved 'surface' of the product in comparison with ordinary hardboard.- As the coat of painting is several cents `per square foot per coat and the cost of the impregnated overlay iszbnly a fraction of a centY per square foot, a considerable-(saving is achieved. The surface effects Vof 'the product are comparable to that of board treated by y immersion or roller application with between 2 and 8% of `dryingoil by weight of the board. It is apparent that the present process will be more economical. The present processfalso compares favourably with the slush overlay process in whichl an overlay of between 25 lbs. and

100 lbs./l000sq.' ft.of board is normally used and in which, in addition, there are higher equipment costs.

It has-beenl found that the foregoing process can be extended to provide'an improved artificial board having Va surface printed with a pattern'sucllasa simulated wood grain.v s j The wood is treated It has been found that, where a pattern is printed on the sheet of paper which is combined with the surface of the board in accordance with the process outlined above, there is excellent resistance to defacement of the pattern by abrasion as compared with post-lamination procedures in which paper having a printed surface is merely adhered to a inished board.

In an experiment conducted to confirm the foregoing, three samples were prepared, namely:

(I) A printed overlay sheet of paper combined with a 1/8 standard base in accordance with the process described in the main disclosure using a linseed oil binder in the proportion of 11/2 lbs. of binder to 1,000 square feet of board.

(II) A similar printed sheet of paper to (I) glued to a finished standard board using ordinary paper mucilage, cold, with slight pressure.

(III) A similar printed sheet of paper to (I) glued to a nished standard board using a latex cement, cold, with pressure to give a good bond.

Samples of each type were tested on a laboratory Taber Abraser, with the wheels of the tester being reground between each sample to provide a fresh surface each time. Observations were carefully made during each test to determine the following end points (measured in revolutions to the nearest as points of comparison:

(A) The point at which the pattern lines rst showed definite signs of wearing off,

(B) The point at which the pattern lines had cornpletely disappeared,

(C) The point at which the overlay paper first showed definite signs of breaking through to the base board, and

(D) The point at which the overlay paper had completely worn olf, leaving the base board showing through.

The results of these tests were as follows:

It will be apparent from the results of these tests that the process of this invention imparts extremely elective resistance to defacement by abrasion to patterns printed on an overlay.

We claim:

1. A process for making hardboard comprising the steps of forming a thick wet lap consisting essentially of coarse fibrous wood pulp and containing the natural lignocellulose, partially dewatering the wet lap to a solids content of 25% to 40% by weight, applying a finished sheet of paper to the surface of said partially dewatered wet lap which comprises the smooth surface of the iinished board, and consolidating the wet lap into hardboard under combined heat and pressure and simultaneously consolidating the sheet of paper therewith.

2. A process as claimed in claim l in which said sheet of paper is substantially dry when it: is applied.

3. A process as claimed in claim l in which said paper prior to application thereof to said wet lap has a pattern printed thereon on the surface opposite the one which is applied to the wet lap.

4. The product produced by the process claimed in claim 1.

5. A process for making hardboard comprising the steps of forming a thick wet lap consisting essentially of coarse fibrous wood pulp and containing the natural lignocellulose, partially dewatering the wet lap to a solids content of 25% to 40% by weight, applying a finished sheet of paper to the surface of said partially dewatered wet lap which comprises the smooth surface of the nished board, applying a layer of binder to a surface of said paper, and consolidating the wet lap to which the sheet of paper and binder have been applied into hardboard under combined heat and pressure and simultaneously consolidating the sheet of paper therewith.

6. A process as claimed in claim 5 which comprises the additional step of curing the consolidated hardboard to strengthen the bond between the paper and the board.

7. A process as claimed in claim 5 in which the binder is drying oil used in a quantity of about l to 5 lbs. to 1,000 sq. ft. of board.

8. A process as claimed in claim 5 in which the binder is applied to the paper before the paper is applied to the wet lap, and that surface of the she-et of paper to which the binder is applied is thereafter applied to the wet lap.

9. A process as claimed in claim 8 in which said paper prior to application thereof to said wet lap has a pattern printed thereon on the surface opposite the one which is applied to the wet lap.

References Cited in the file of this patent UNITED STATES PATENTS 242,253 Benton May 31, 1881 513,017 Howard Jan. 16, 1894 695,787 Brown Mar. 18, 1902 793,832 Engelmann July 4, 1905 1,680,896 Marr Aug. 14, 1928 1,941,536 Boehm Jan. 2, 1934 1,995,145 Frost Mar. 19, 1935 2,077,714 Rozema Apr. 20, 1937 2,161,655 Ellis June 6, 1939 2,167,440 Mason July 25, 1939 2,348,081 Linzell May 2, 1944

Claims (1)

1. A PROCESS FOR MAKING HARDBOARD COMPRISING THE STEPS OF FORMING A THICK WET LAP CONSISTING ESSENTIALLY OF COARSE FIBROUS WOOD PULP AND CONTAINING THE NATURAL LIGNOCELLULOSE, PARTIALLY DEWATERING THE WET LAP TO A SOLIDS CONTENT OF 25% TO 40% BY WEIGHT, APPLYING A FINISHED SHEET OF PAPER TO THE SURFACE OF SAID PARTIALLY DEWARTED WET LAP WHICH COMPRISES THE SMOOTH SURFACE OF THE FINISHED BOARD, AND CONSOLIDATING THE WET LAP INTO HARDBOARD UNDER COMBINED HEAT AND PRESSURE AND SIMULTANEOUSLY CONSOLIDATING THE SHEET OF PAPER THEREWITH.

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