US2872337A

US2872337A - Method of coating a felted fibrous mat

Info

Publication number: US2872337A
Application number: US401322A
Authority: US
Inventors: Clark C Heritage; James R Roberts
Original assignee: Weyerhaeuser Timber Co
Current assignee: Weyerhaeuser Timber Co
Priority date: 1953-12-30
Filing date: 1953-12-30
Publication date: 1959-02-03
Anticipated expiration: 1976-02-03

Description

Feb. 3, 1959 c. c. HERITAGE ET AL 2,872,337

METHOD oF coATING A FELTED FIBRoUs MAT Filed Deo. 30. 1953 2 Sheets-Sheet 1 Nl QQQS Feb. 3, 1959 c. c. HERITAGE ET AL 2,872,337

METHOD oF comme 'A FELTED FIBRoUs MAT v Filed Dec. 30. 1955' 2 Sheets-Sheet 2 IN VEN TORS C l ark CHerjgge cmd BY Jam e5 RRobers fw mrnon oF `coArrNG A FELTED FrBRoUs MAT "Clark C. Heritage, Tacoma, and James R. Roberts, .Longview, Wash., assignors to Weyerhaeuser Timber 'Conv pany, Tacoma, Wash., a corporation of Washmgton Application December 30, 1953, Serial No. 401,322

i 8 Claims. (Cl. 117-11) Thisinvention relates to surface treated consolidated products such as, for example, coated hardboard and contoured objects made from wood fibers, and to a process for making such products.

In the conventional wet'processes for making bervboard, Wood or other lignocellulose is comminuted,` mixed felt various treating agents for imparting desiredproperties to the board product. This is possible in the case of softboard since the mat is dried without restraint and the treating agents which have been applied to the surface therefore remain substantially in situ. Y K

However, if it is desired to apply treated agents to wet process felts which are to be hot-pressed for the manufacture of hardboard or contoured products, it obviously becomes impossible to apply the agent to the felt surface before pressure is applied. This is for the reason that the application of pressure causes the treating agent to strike into the felt, or to be squeezed out of it. As a result, the treating agent either is removed in large measure, or re-distributed so that it no longer accomplishes the contemplated purpose.

Accordingly, if it is desired to place a surface treating agent such as resin or wax on aA hot-pressed fiberboard, the pressed board must beimmersed in abath of the agent, or passed between coating rollers, or sprayed with the agent, after which it is baked or dried again to fix the agent on the board surface. These extra processing steps Lobviously add substantially to the cost of the finished product.

We now have discovered that surface treated consolidated products, such as hardboard and contoured, consolidated, fibrous structures may be made by a simplified procedure which requires `but a single heating operation. In

lected surface areas of the felt without disturbing the felted relationship vof the surfaceparticles, after which the felt is consolidated to a predetermined density by the application Iof heat and pressure. This forms a uniform,

rigid consolidated product in which the surface treating agent remains uniformly distributed over the selected surface areas for optimum beneiciation of the same.

Thus incontrast to the wet process, the surface treating agent may be applied directly to the felt without excessive striking in and without being washed away during pressing since there is insunicient moisture in the felt to serve nited States Patent 12,872,337 Patented Feb. 3, 1959 a costly, time-consuming, and less eicient post-press treating operation.

The manner in which the foregoing novel procedure is ,eflectuated will be described with particular reference to the drawings wherein:

Figure l is a schematic view of one form of apparatus which may be used in the preparation of wood fibers for application in the hereindescribed procedure and for adjusting their moisture content to the necessary level; and

Figure 2 is a schematic view of one form of felting and surface treating apparatus which may be employed in forming the fibers into a surface treated felt which subsequently may be hot-pressed to form a consolidated product with the desired surface properties.

v The raw material for practicing the process of the present invention broadly comprises lignocellulose materials, such as corn stalks, bagasse, straw and the like, but preferably Wood of various tree species in the form of chips. In the first step of the invention, namely, the reduction of the wood to fibrous form, various conventional delibrators such as the Bauer, the Allis Chalmers, and the MacMillan defibrators, may be employed. Also, although less desirably, apparatus designed to reduce wood to particle or granular form, such as sawdust or milled chips, may be employed. A particularly suitable type of reducing apparatus, however, is that known as the Asplund debrator, the construction of which is described in U. S. Patent 2,045,851 to Asplund.

Thus wood in the form of chips may be introduced into a bin 10 from which it is fed by screw conveyorf12 into the horizontal, steam heated preheater 14 of an Asplund defibrator. `The preheater has on its infeed side a constriction 16. It is fed with steam under pressure through Y line 18, which also may introduce steam into the defibrating chamber.

The chips after traversing the horizontal preheater pass into the vertical preheater 20, whence they Vare forced through the spool piece 22 into the defibrating chamber 24. There, having been softened by the steam environment present in the apparatus, they are fed between relatively

rotatable discs

26, 28, which rub and abrade them to form a fibrous product consisting principally of ultimate fibers' in the form of individual tracheids, together with a minor proportion of flexible, opened up bundles of fibers.

In order to obtain the desired result during defibering, i. e. the reduction of the lignocellulose to the form of individual tracheids with a minor proportion of flexible bundles of the same without chemically degrading the wood, it is necessary to control the conditions within the defibrator within carefully defined limits, which may vary for each specific material. These conditions are met when wood chips are defibered while subjecting them to an atmosphere of steam maintained at between 50 and200 p. s. i. g., and corresponding temperatures for saturated steam, for periods of time ranging from 1/4 minute to 30 minutes, the lower limit of the pressure-temperature range applying to the higher limit of the time range and vice versa. Preferred conditions are between 80 and 160 p. s. i. g. for from V2 minute to 6 minutes. When the lignocellulose is defibered under these conditions, a major proportion of substantially ultimate bers or individual l3 traeheids is produced with minimum degradation of the wood substance.

The fibrous product formed in the deiibering chamber is discharged through an oriiice 30. The discharged ber enters aiii'st conduit 32 at substantially the machine tempe'rature and ina moist condition, its moisture content being between 30% and 100% by weight (dry basis). Since it has been forced suddenly from a region of relatively high pressure to one of substantially atmospheric pressure, there Yis a marked lowering of the temperature as a result :of the instantaneous and therefore near adiabatic expansion of the steam. The heat thus liberated assists in drying the fibers.

lAlso, the fibers are in a condition of Igreat turbulence andumay therefore now be mixed effectiveiy with additive materials. vHence, a thermosetting resinous binder, if such is to be incorporated, may be Vintroduced in a pumped, metered feed through line'y Other materials, "such as thermoplastic binders, sizingimaterials, iire-proofing agents andthe like, maybe introduced at this point, i

aswell `as at other suitable points, as for example, in the preheater, vialine 36, or ahead kof the deiibering discs via line 38. T he choice of the point of addition of these materials is determined by their properties and the properties desired in the final product.

' In orderv to dry themoist mixture of fiber and binder as Well as to yadvance to the optimum extent any ther- 'mosetting resin which may have been added, but without rendering it inert and infusible, the fiber-binder mixture formedjust beyond orifice 30 is passed rapidly through the elongated conduit 32 where it is thoroughly mixed,

vcboledby the expansion of the steam as well as byradiation from'the conduit, partially dried, and its resin con- Vtent only partially cured because of the short duration 'of passage through the conduit. From conduit 32 the mixture passes through steam separator 40 where some further cooling may occur, after which it enters a second 'conduit 42.

The latter communicates with a heating chamber 44 Vsupplied with air or other dehydrating gases, such as nitrogen or ue gas, heated if necessary in heater 46 and forced into the conduit by means of fanV 48. The air supplied by this heater is at a temperature sufiicient to raise the temperature ofthe mixture to a level at which itis dried to the critical moisture content, for thepurp'oses ofthe present invention, of between and 40%,-pref- A'erably of between 10% and 30% by weight. It also effectuates some further advancement of the resin,- but without'l destroying its bonding and fusible qualities. Y

lTheVv dried mixture is separated from the entraining air in "cyclone 50 where it is cooled rapidiy. VF[his prevents further advancement of the resin. The fiber product wither without added resin then is deposited onconveyor 52-for conveyance to storage, or tothe felting means, or to a fiber 'fractionating means 54. The latterhas for its j function the Vremoval of pieces that arefnot substantially yultirriateA fibers and thereby produces a product which from the standpoints of particle size and particle uniformity Aapproaches chemical pulp. This is important :subsequently inthe procedure in providing uniform feiting with no low-strength islands and permits uniform mats to be laid down.

The-fractionation may be eectuated in a series of `vibrating screens, a winnower, or one or more whizzers (Crites U. S. Reissue 20,543). vOne of the fractions producedmay comprise a lrelatively `small proportion of fines,

which may be discarded. A second fraction consists of over-size particles or chunks which may be discarded,

re-'commiiiuted in a second renner (prior tomixing with ltheV acceptable fraction), 'or recycled via conduit 56 to hopper for feeding again into'the defibrator. Still l'another fraction comprises the major proportion of the 4material fed and 'constitutes the acceptable fraction for Vthe 'purposes of the presentinvention. The acceptable fraction passes in a conduit 5S, to a conduit 59 which yconveysit vtothe-felting apparatus. AConduits 58 may in a sufficiently self-sustaining form may be transported,

stored, and 'then pressed at a future date. inthe alterno.- tive, the fibers may be shaped by pneumatic blowing or otherwise into contoured forms which may be pressed immediately or stored for pressing at a later date, the

- surface treating agent being applied in the latter case either before or after storage.

Where a at mat to be used in the fabrication of hardboard is desired, the fiber preferably is entrained in air and impact felted in the apparatus-illustrated in Figure 2. In accordance with this embodiment, the iiber from fractionator 54 is conveyed by conduit 59 to belt 60. This belt has lassociated with it a weighing mechanism 62, so that the combination comprises a weighing feeder for feeding a measured amount of fiber into a hopper 64.

Hopper 64 communicates with a -conduit 66 having therein a chute 68, positioned for feeding additive materials such as extraneous size or binder if these are to be added at this point in the ow. The additive materials are fed to chute 68 by means of a suitable weighing and feeding mechanism including the weighing unit 70 which deposits the additive upon a conveyor 72, which in turn .empties into chute 68.

Suction is applied to conduit 66 by means of a rotary fan 74 which drives the mixture of ber and additives through an elongated conduit 76 where mixing of the fiber with the additives occurs. Conduit 76 in turn empties into a housing 78 which serves as an expansion conduit for the air-entrained fibrous mixture. Hence, it serves the functions of reducing the velocities of the fibers, minimizing felting in the housing, and of equalizing the vair stream over the discharge area of the housing. The bottom or discharge opening of housing 78 may be extended by a suitable tubular means such as head-box 80. The length of the head-box may be varied to suit particular installations, since it serves as a connecting link between housing 78 and a felting head 82 connected to the head-box at its discharge end.

Felting head 82 comprises a semi-cylindrical member disposed substantially at right angles to themachine direction. A suitable arc,` for example, an arc of about 100 of its periphery is perforated symmetrically with openings having diam'eters vcalculated to pass individualized iibers of the air-entrained fibrous mass fed thereto under pressure from fan 74. The openings serve the function of breaking up any ber clumps and of passing a uniform rain of individual ibers to the exterior.

To assist in breaking up the fiber clumps and transmitting them through the openings in the felting head, there is provided agitating means which in a preferred embodiment comprises the paddle-wheel 86 mounted coaxially with the felting head and driven by a suitable power means. v

The individual fibers 'passing through the perforations are driven in a steady stream by the force of the entraining air against a foraminous support member which preferably is a continuous screen 90. Screen 90 is driven by suitable means at a rate correlated with the rate of deposition of the fibers to form a felt vof the desired thickness.

` The felting of the bers on screen 90 is assisted by establishing an independently controllable vacuum be neath the screen. To this end there is provided a suction box 92 of suitable dimensions. It communicates with a conduit 94 which in turn leadsto a fan 96, which exhausts through conduit 98 into a solidsseparator such as cyclone 1100.

The bers thus are formed intoa continuons, uniform mat or felt 102 by the co-action of the driving force of the pressure stream in the fclting head above the screen and the suction stream in the suction box below the screen. The felt is contained within and dimensioned laterally by a pair of opposed vertical side walls, one of which is indicated at 104, stationed on opposite sides of the screen and connected by a vertical end wall 106.

After the felt leaves the forming area, it passes between the

pressing rollers

108, 110 which effect its partial consolidation and make it self sustaining. It then passes the cut-off saws, represented schematically at 111, which cut it into

sections

112, 113 of substantially equal lengths.

The mat sections pass onto a downwardly inclined transfer belt 114 driven in the outfeed direction at a rate substantially equal' to the rate of travel of the conveying wire 90. This transfers the sections to .a supporting member 120 which preferably comprises a sheet of material at least as wide as the mat sections and inclined down- Wardly in the outfeed direction at substantially the same angle as transfer belt 114.

At this stage a surface treating agent may be applied to advantage to selected surface areas of the mat. It may be desirable, for example, to apply a thermosetting resinous material for imparting a glossy surface to the pressed board product. This is useful in a multitude of applications, as where the boards are to be used as cladding for plywood or lumber. Also, it hardens the surface, making it more durable and resistant to abrasion, and improves the water repellency and stability of the product.

Although various thermosetting resins may' be em ployed for this purpose, such as the phenol-aldehyde resins, the urea-aldehyde resins, the melamine resins, and the like, the thermosetting phenol-formaldehyde resins are preferred. They may be applied in amounts of from 0.01 to 0.20, preferably from 0.03 to 0.12 ounce per squarev foot of mat surface. They may be sprinkled onv in powder form, but preferably are applied in the form of' their aqueous, alkali-stabilized' solutions, or as solutions. of the resin solids in an organic solvent such as alcohol- Alternatively, other treating agents may be applied in place of or in addition to the thermosetting resin. For example, various thermoplastic resins such as the vinyl resins, the glyptal resins, the bitumens and the like may beemployed. Also, if desired, various waxes, tempering agents such as the drying oils, thyotropic materials, sulfur, asphalt, inorganic or organic compounds used .as fireor mold-proofing agents, and the like, may be applied at this stage.

These and other surface treating agents may be em ployed in uid form, as in the form of their solutions,l suspensions, or emulsions using water, alcohol or other liquid carrying medium. If desired, and where possible, they may be applied in molten form. Still further, they` may be applied in certain cases in the form of granules or dusts.

Where a liquid treating agent is to be applied, the applicating means used for applying it to the top surfaces of the mat may comprise in general one or more spraying: units such as spray heads 122, 124. The applicating: means for applying the agent to the undersurface of the mat may be installed and operated as follows:

Cooperating with transfer belt 114 and supportingv member 120 is means for conveying the mat away for further processing. In the illustrated form, the convey ing means comprises an endless belt 126 stationed below the latter two members. It extends outwardly therefrom. a spaced distance below the lower end of the supporting; member 120, and is driven in the outfeed direction at a. rate substantially the same as the rate of travel of both. the felting wire 90 and the transfer belt 114.

Conveying belt 126 serves a three-fold function. First, as has been noted, it conveys the mat sections away from4 the supporting member for further treatment. Secondly, if the subsequent treatment is to be a pressing operation used to produce a hardboard which is smooth onbotlt sides, it affords a means for placing below the mat one of the caul plates indicated at 128, 130, which have dimensions substantially equal to those of the

mat sections

112, 113 immediately above. This may be accomplished simply by placing the caul plates edge to edge on the upper end of conveyor belt 126. Then as each mat section leaves supporting member it is deposited on the caul plate directly beneath and in registry with it. An upper caul plate then may be placed on top of each mat section to form an assembly ready for introduction into a hot press.

The third function served by conveying belt 126 comprises providing an opportunity in cooperation with the supporting plate 120 from which it is vertically spaced apart for applying treating agent to the under side of the mat efficiently and without disturbing or disarranging the mat. The agent thus applied may be the same or different from the coating agent applied to the top surface of the mat. Any suitable type of apparatus may be used for this purpose, such as the spray heads ,132 illustrated schematically in the drawings. Whatever their construction, they are stationed in such a manner as to directa spray of material against the underside of the mat sections in the area exposed as they transfer from supper-ting plate 120 to the caul plates on conveying belt 126.

Where the treating agent is applied to the mat surfaces in solid form, it may be sprinkled or dusted on the selected ysurfaces or on conveying or supporting means employed ifor conveying or supporting the mats. Thus, it may be .sprinkled or dusted uniformly on the surfaces of conveying belts or of caul plates to be used for conveying or supporting the mats.

Whatever means employed for applying the treating agent, it will be .apparent that the agent penetrates the surface of the belt uniformly and without disturbing the interfelted relationship of the component particles of the felt and without penetrating to the interior of the felt. Where a coating agent is applied, the limited penetration of this agent into the felt imparts to the outer surface of the finished product a permanent glaze which is integrated with the base structure, as opposed to being a surface film or lamina.

Finally, the mat sections are introduced into a hot press such as the one illustrated schematically in the drawings .and comprising an upper platen 134 and a lower platen 136. These may or may not be used with separate caul plates as desired. In an illustrative procedure, the sandwich assembly comprising the mat section 138, the upper caul plate and the lower caul plate 142 may be introduced between the platens of the press and pressed to the desired density.

Although the pressing schedule employed may be varied to suit the type of hardboard to be produced and the character of the treating agent applied thereto, in general, it'comprises pressing the mat at from 50 to 1500 p. s. i. at C. to 230 C. for from 2 to 30 minutes. This produces the finished, surface treated board.

From the foregoing, it is apparent that we have developed an eflcient process for treating the surfaces of consolidated products such as hardboard and contoured brous articles. This procedure eliminates the necessity of using post-press treating operations such as immersion of the product in the treating agent followed by drying or baking. On the contrary, the treating .agent may be applied directly to the felt before pressing, and the treated surface is formed contemporaneously with the densified product. Also, during this procedure the treating agent penetrates a limited and controlled distance into the felt, without disturbing the component particles of the felt, thereby forming a final product having a uniformly treated, integrated surface.

It is to be understood that the form of our invention, herewith shown and described, is to be taken as a preferr'ed 4'example of! the same; and that various changes in theshape, size/and .arrangement of parts may-be resorted to, without departing from the spirit Vof our invention, or the scope of the subjoined claims.

Having now'described our invention in preferred embodiments what we'clairn as new and desire to protect by Letters Patent is:

1. The process ofrnaking a coated-consolidated product in a single pressing'vstep which comprises forming deiiberized-wood lhaving a moisture content "ot kfrom 5 40% by weight into a felted'mat by the dry felting impact procedure, distributing on the surface coating agent, and lhotpressingthe resulting product forconsolidating it to a predetermined-shapeand density.

2. The process :of claim 1 wherein thetcoating agent comprises a thermosetting resin.

3. The processof yclaim 2 vWhereinthe thermosetting resin is a condensation product of a phenoland an alde- 4L The process'of claim l-vwherein the coating agent comprises a drying oil.

5. The product produced by the process which comprises forming deberized wood having a moisture content of from 5-40% by weight intoI afelted mat by the dry felting impact procedure, distributing on the surface 'of the mat a predetermined quantity of a surface coating agent, and hot pressing the resulting product for consolidating it to a predetermined shape and density.

6. The product of claim 5 wherein the coating agent comprises a thermosetting resin.

7. The product of claim 6 wherein the thermosetting resin is a condensation product of a phenol and an aldehyde.

8. The product of claim 5 wherein the coating agent comprises a drying oil.

References Cited in the file of this patent UNITED STATES PATENTS 2,206,056 Sheesley e Iuly 2, 1940 2,503,407 Perry Apr. 11, 17950 2,545,952 Goldman v -e Mar. 20, 1951 2,790,736 McLaughlin Apr. 30, 1957

Claims

1. THE PROCESS OF MAKING A COATED CONSOLIDATED PRODUCT IN A SINGLE PRESSING STEP WHICH COMPRISES FORMING DEFIBERIZED WOOD HAVING A MOISTURE CONTENT OF FROM 540% BY WEIGHT INTO A FELTED MAT BY THE DRY FELTING IMPACT PROCEDURE, DISTRIBUTING ON THE SURFACE COATING AGENT, AND HOT PRESSING THE RESULTING PRODUCT FOR CONSOLIDATING IT TO A PREDETERMINED SHAPE AND DENSITY.