US3878020A

US3878020A - Method of making plywood cores

Info

Publication number: US3878020A
Application number: US351225A
Authority: US
Inventors: James Edward Huffaker; Brian Douglas Dillon
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1971-01-11
Filing date: 1973-04-16
Publication date: 1975-04-15
Anticipated expiration: 1992-04-15

Abstract

Method of making plywood veneer cores or sheets by continuously bringing a succession of thin random width wood veneer sections of substantially the same length into edge-to-edge contact, extruding a plurality of continuous beads of a hot melt adhesive onto the upper surface of each of the abutting sections and simultaneously pressing a strong, porous paper tape onto each of the adhesive beads in such a manner that the adhesive is caused to adhere to the undersurface of each tape, whereby strong adhesive bonds are formed between each of the tapes and the underlying surfaces of each of the sections. Alternatively, the tapes may be precoated with the adhesive and continuously applied to the sections with the adhesive side down and the adhesive melted and reactivated in situ by pressing the tape into contact with the sections by means of a heated roll. In either case the resulting product is a multi-section thin veneer core sheet which unexpectedly has sufficient strength and other desirable properties to enable it to be cut into 4 X 8 foot sheets or plys for use in standard plywood laminating operations.

Description

United States Patent 1 Hufiaker et al.

[ METHOD OF MAKING PLYWOOD CORES [75] Inventors: James Edward Hufiaker; Brian Douglas Dillon, both of Kingsport, Tenn.

[73] Assignee: Eastman Kodak Company,

Rochester, N.Y.

[22] Filed: Apr. 16, 1973 [2]] Appl. No.: 351,225

Related US. Application Data [63] Continuation of Ser. No. 105,397, .Ian. 11, 1971,

Defensive Publication T896,014.

[52] US. Cl. 156/291; 156/295; 156/304;

156/548; 161/37; 161/56; 161/148 [51] Int. Cl. B32b 7/14 [58] Field of Search 156/291, 304, 251, 295,

[56] References Cited UNITED STATES PATENTS 884,905 4/1908 Dennis 156/304 3,445.313 5/1969 Clausen 156/498 X Primary ExaminerWilliam A. Powell Attorney, Agent, or Firm-Malcolm G. Dunn; Charles L. Good 1 Apr. 15, 1975 [57] ABSTRACT Method of making plywood veneer cores or sheets by continuously bringing a succession of thin random width wood veneer sections of substantially the same length into edge-to-edge contact, extruding a plurality of continuous beads of a hot melt adhesive onto the upper surface of each of the abutting sections and simultaneously pressing a strong, porous paper tape onto each of the adhesive beads in such a manner that the adhesive is caused to adhere to the undersurface of each tape, whereby strong adhesive bonds are formed between each of the tapes and the underlying surfaces of each of the sections. Alternatively, the tapes may be precoated with the adhesive and continuously applied to the sections with the adhesive side down and the adhesive melted and reactivated in situ by pressing the tape into contact with the sections by means of a heated r011. In either case the resulting product is a multi-section thin veneer core sheet which unexpectedly has sufficient strength and other desirable properties to enable it to be cut into 4 X 8 foot sheets or plys for use in standard plywood laminating operations.

5 Claims, 3 Drawing Figures CR OWDER SECTION sumlq z METHOD OF MAKING PLYWOOD CORES This application is a continuation of copending application Ser, No. 105,397 filed Jan. ll, 1971, now Defensive Publication No. T896,0l4 published Mar. 7, 1972.

This invention relates to the manufacture of plywood and more particularly to the manufacture of sheets useful plywood cores. Still more particularly, the invention relates to a means and method of making plywood cores by permanently securing abutting sections of thin wood veneer of varying widths edge-to-edge in such a way that plys of the desired lengths and widths may be cut from the resulting multi-section sheet and thereafter satisfactorily employed as core sheets in a plywood laminating operation.

As is well known by those skilled in the art to which the present invention relates, in the early development of plywood manufacture many phases of the manufacturing process required a considerable number of operators who performed many manual operations from the cutting, preparation and sizing of the wood veneers and other elements to be employed in the finished product, to the final steps of the laminating phase of the process. In recent years, an increasing number of the various steps in the overall manufacturing process have been automated, mechanized and improved in other ways to the extent that production per man hour of labor has been increased.

One of the steps in the modernized method of plywood manufacture involves the preparation of sheets to be used as centers or cores which are thin wood veneer strips which are placed between two or more other wooden strips or plys and laminated or adhesively joined together, generally by the employment of a phenol-formaldehyde or other heat-hardening resin. These thin veneer cores are produced by skiving a thin wood layer or sheet from a selected log. This is done by clamping or otherwise securing the log in a device designed and functioning to rotate the log against the cutting edge of a fixed knife or similar skiving element. Since logs employed for this purpose are of varying diameter, the skived pieces of veneer will have varying lengths and, since plywood is generally manufactured in 4 X 8 foot pieces, it follows that when the skived ma terial does not conform to these dimensions there will be a certain amount of excess material at either or both ends of the skived sheet and that this material will be of varying widths and must be utilized in order to make the overall manufacturing process economically feasible. Accordingly, it has been the practice in the indus-.

try to utilize these random width pieces by cutting them into pieces approximately 8 feet long, providing them with straight lengthwise edges and thereafter bringing them into edge-to-edge contact and securing them inline by some sort of. connecting or linking means, thereby producing what is, in effect, a continuous or unitary sheet of thin veneer core material from which plys or cores of the desired 4 X 8 foot dimensions may be cut and stacked for future use in a plywood manufacturing operation.

The principal mechanical steps involved in the manufacture of plywood veneer cores from odd random width pieces such as referred to above involves the following steps: The random width veneer pieces are cut to approximately an 8 foot length, and preferably a little longer, to allow for ultimate trimming. They are then introduced sidewise one at a time into a crowden This is a machine which supports these thin veneer sheets horizontally between two sets of endless chain belts, similar in construction to bicycle chains, and operating in parallel. As the pieces enter the small space between the moving belts they are continuously forced or crowded into in-line, edge-to-edge contact with one another. The sheets. still in close edge-to-edge contact, are then picked up by an endless chain belt or similar conveyor which carries them underneath a device which continuously applies to the upper surfaces of the veneer pieces a plurality of adhesiveimpregnated strings, the function of which it to hold the respective veneer sections together in permanent edgeto-edge contact. The strings are so disposed on the multi-section material that when it is later cut into 4 X 8 foot plys there will be a segment of connecting material along and in proximity to the outer edges of each of the cut sheets or plys. Generally, this will mean that at least four strings are laid down on each 8 foot length of random width veneer material so as to provide that two 4 X 8 foot pieces may be obtained from the multi-section material as it is cut in the middle as it progresses through the joining operation. The 4 X 8 foot pieces cut in this manner are continuously lifted from the conveyor one by one by vacuum lifters are stacked for future use in a plywood laminating operation,

Although the process of securing pieces of wood veneer to make a unitary core of material, according to the prior art practices described above, would appear to be very simple operation, experience has shown that in actual practice it is extremely difficult to obtain a satisfactory and usable multi-section core material which will be free from such imperfections as lumps, ridges and other defects, and at the same time have sufficient strength to withstand the stresses and strains to which the material will later be subjected in normal handling and use.

As indicated above, one of the expedients heretofore employed to connect random width wood veneer sections is to connect them with a fiberglass, nylon or other type of rope or.string impregnated or coated with a hot melt adhesive. In this method, the adhesiveimpregnated or coated rope or string is deposited on the upper surfaces of the sections in parallel lines and hot pressed against the wood surface. While this method has met with some success it has the serious disadvantage that the adhesive as usually applied does not spread out on the surface of the wood sections as effectively as desired. Furthermore, since the fibrous material is in the form of a rope or string there may be a pronounced tendency to form an unsightly ridge when another plywood sheet is superimposed on and glued to a core material, the veneer sections of which are joined in this manner. In other words, in terms of the art, the line of the applied adhesive-impregnated rope or string may be telegraphed to the surface of the final laminated plywood product, thus making it substantially unacceptable for many practical purposes.

Another means of adhesively joining random width core sections has been to apply adhesive tapes along the seams formed by the abutting edges of the veneer sections but this expedient has not proved to be reasonably satisfactory because of insufficient joint strength due to the limited areas of adhesive in contact with the surfaces of the abutting veneer sections.

Still other methods ofjoining random width sheets of veneer core material involves sewing or stapling the adjoining sections together, but these methods have also found to be too slow or cumbersome or otherwise unsatisfactory or impractical. Furthermore, the finished core materials with veneer sections secured by these methods generally lack the strength and integrity necessary to make them commercially useful.

It has also been proposed simply to apply a plurality of short beads or strings of advesive itself to connect abutting edges of adjacent veneer sections but this expedient has also proved unsatisfactory because the deposited adhesive beads in molten or semi-solid condition were found to have insufficient tensile strength to hold the abutted contacting edges of the veneer sections evenly and flatly together at the line of contact while the adhesive is cooling down.

In summary, it may be said that all of the above mentioned attempts to solve the problem of effectively securing abutted random width veneer sections together in-line to produce a unitary and usable veneer core product have presented problems, not only because of the reasons stated above, but also because, when using such expedients, the procedures are usually cumbersome and the material costs too high to be economically feasible.

As will be more fully set forth hereinafter, the present invention provides a simple, effective, easily operated and economical method of adhesively securing a succession of abutted random width core veneer sections in a continuous manner while at the same time overcoming all of the various disadvantages pointed out as concommitants of prior art practice. Furthermore, as will be evident as the description'proceeds, the method of the present invention can be operated rapidly, uniformly and automatically by the employment of plywood manufacturing machinery currently used in the industry with only slight modifications or additions which can be simply and, easily made.

The present invention therefore has as its principal object to provide an improved method for manufacturing plywood core material from random width sections of this wood veneer.

Another object is to provide a means and method for continuously joining a succession of random width plywood veneer sections edge-to-edge by adhesive means which provides unexpectedly advantageous resistance to the stresses and strains to which the material may later be subjected in normal handling and use in a plywood manufacturing operation.

Another object is to provide an improved plywood veneer core composed of random width sections of thin wood veneer which are secured edge-to-edge by an inline adhesive means which has no adverse effect upon any subsequent gluing or laminating operation to whichthe core material may be subjected in the manufacture of plywood products.

A further object is to provide an improved plywood product composed of at least one ply of a core composed of multi-section thin wood veneers joined together edge-to-edge by a hot melt adhesive adhered to one surface of the core and to the under surface of a porous paper tape, said core being interposed between and adhered to each of two other wood plys by means of a heat-hardening adhesive, said. plywood product being particularly characterized by the fact that the tape and its underlying adhesive are invisible in the product and have no adverse effect on the distribution or adhesivity of the laminating adhesive.

Other objects appear elsewhere herein.

These objects are accomplished by the following invention which, in one of its preferred embodiments, comprises feeding a succession of random width thin wood veneer sections, preferably of rectangular shape and having straight lengthwise edges, into a crowder, crowding these sections together sidewise, in-line and in close abutting edge-to-edge contact and then conveying the abutted sections onto a'conveying means, such as an endless belt conveyor, then underneath an adhesive depositing means which continuously extrudes a plurality of molten hot melt adhesive beads onto the upper surfaces of the abutted sections. The assembled material is immediately thereafter conveyed underneath a paper tape applying means from which a plurality of narrow porous paper tapes is fed into contact with and superimposed on each of the molten adhesive beads, after which pressure is applied to the upper surface of each of the tapes by means of a pressure roll in contact with the upper surface of each tape at its point of contact with each adhesive bead. The action of the pressure roll serves to spread each of the adhesive beads across substantially the entire under surface of each individual tape in such manner that each of the tapes will be adhered to the upper surface of the wood veneer strips or sections and will at the same time fill any irregularities in the underlying wood surfaces. This procedure produces what is an essentially continuous sheet, but actually consisting of a succession of abutted randon width veneer sections held together inline by the applied tapes.

The pressure roll may be internally cooled by appropriate means in order to facilitate solidification of the adhesive underlying the tapes. Under some circumstances, the roll may be heated to maintain the molten adhesive at the proper application consistency. The resulting veneer sheet is then cut into 4 X 8 foot lengths,

each of which is removed from the conveying means by contact with the upper surfaces of the veneer sections.

In this case, the pressure roll will be heated to reactivate the adhesive coating of each tape and thus cause the tape to adhere to the veneer sections as they pass underneath the roll. When using such precoated tapes, the tapes will be supplied from supply rolls so positioned with respect to the heated roll as to provide that each tape will be in contact with the surface of the hot roll for a sufficient length of time to permit heat transferred from the roll to melt and reactivate the adhesive coating before it contacts the wood surfaces. After the tapes are applied in this manner, the resulting multisection veneer core product is carried into a cutter and cut into 4 X 8 foot plys which are then removed from the conveyor and stacked for use in a plywood laminating operation as previously described.

Of the two methods of operation described above the method of first applying a molten adhesive and then covering it with a paper tape and pressing it into contact with the veneer sections is preferred since it is more economical from the standpoint of time and labor saving than is the use of precoated tapes, especially if one takes into consideration the time and effort re quired to prepare such tapes as a part of the overall manufacturing process.

The invention is characterized by the fact that when random width veneer sections are joined by either of the methods described above, the resulting core prod uct unexpectedly has sufficient strength to withstand the stresses and strains to which it will be subjected when cut into 4 X 8 foot plys, stacked and subsequently employed in a plywood laminating operation. The invention is further particularly distinguished by the fact that the tape and adhesive as applied to the veneer provides minimum interference with the bonding action of phenol-formaldehyde or other heat-hardening laminating adhesives when the core is employed in a plywood laminating operation. The present invention also has the outstanding advantage that no telltale ridges revealing the location of the underlying adhesives bonds are telegraphed" to the surfaces of the final laminated product. One further and outstanding characteristic of this invention is than when applied by either of the manipulative procedures described above, the adhesive fills any irregularities which may be present in the wood surfaces at the areas of contact, thereby precluding formation of undesirable let-gos between wood and the adhesive.

The plywood core material of this invention may be produced by joining random width wood veneers cut from any type of wood suitable for use, in the plywood industry. Generally, the material will be produced from soft wood such as southern pine, fir, cedar and the like. However, any of the wood referred to in Table 2 of the brochure entitled US. Production Standard PS 1-66 (1966) issued by the Products & Standard Section of the National Bureau of Standards, Washington, D.C., may be used for this purpose.

Adhesives preferred for use in practicing the present invention are of the hot melt type, the compositions of which are well known to those skilled in the art. Typical examples of such adhesive compositions are those based on low molecular weight polymers such as polyethylene, ethylene vinyl acetate copolymers and polyvinyl acetate. These compositions advantageously have a Brookfield viscosity within the rage of 250 50,000 centipoises at 375F. and an adhesivity when applied to the wood surface sufficient to preclude delamination of the veneer from the paper tape under cutting and handling conditions and when the 4 X 8 foot core sections are employed in an actual plywood lamination operation.

In accordance with one aspect of this invention, the adhesive is advantageously melted and maintained in a molten condition at the point of contact with the wood surfaces at a temperature within the range of 300 450F. and preferably at a temperature within a range of 350 400F. The actual temperature employed in any given application will of course depend upon the melt temperature of the selected adhesive and the particular operating conditions employed. Thus, when operating at relatively high linear speeds it may be necessary to raise the temperature of the applied melt over what would normally be used in slower linear speeds of operation since the adhesive material must have a sufficiently low viscosity to be applied satisfactorily to a rapidly moving wood surface.

In a preferred form of this invention in which a bead of the adhesive material in molten form is continuously laid down on the upper surface of the core material and a paper tape is superimposed on the adhesive, the tape can conveniently have a width within the range of A; inch to 1 /8 inches. The paper of which the tape is composed must have sufficient tensile and tear strengths to hold the pieces of random width veneers together edgeto-edge in 4 X 8 foot core configurations under the longitudinal and transverse stresses and strains normally encountered in cutting the material to this size and in using it is a plywood laminating operation. No hard and fast rule can be laid down as to the actual width of the paper tape nor the tensile and tear strengths except as specified above. In general, it may be said that the paper must be of such composition and structure as to provide a strong bond between the adhesive and itself in order to preclude delamination of the wood and paper under normal handling conditions. In preferred embodiments of this invention a porous paper tape is employed. However, in some cases a non-porous tape may be employed. If such a non-porous tape is used, it will preferably have a narrower width than would be the case when employing a porous material, in order to provide minimum interference with the wood-to-wood bonding by the heat-hardening adhesive used in the laminating operation. In the accompanying drawings,

FIG. 1 is a perspective view in the nature of a flow sheet illustrating the overall process of making plywood veneer cores in accordance with the invention.

FIG. 2 is a perspective view of a three component plywood product illustrating the use as the center or core of a ply of core material produced in accordance with the invention and adhesively joined or laminated, respectively, to a top ply and to a bottom ply.

FIG. 3 is a perspective view similar to that of FIG. 2 and illustrating the use in a two core, five ply construction of two plys of core material produced in accordance with the invention.

Referring to the drawings, numeral 1 designates a supporting and conveying assembly of conventional design employed in the plywood industry for making plywood veneers or cores from random width pieces or sections of this wood veneer. The mechanism shown comprises three principal sections, namely, a crowder section, an adhesive application section and a cutting section. Numerals 2, 3 and 4 designate the pieces of thin wood veneer approximately 8 feet long and of random widths entering a crowder (not fully shown) which is in the form of two sets of endless belt type link chains (not shown but similar in construction to bicycle chains), one set being disposed underneath and supporting the random width plywood sections 2, 3 and 4 as they enter the crowder section, the other set being disposed above and resting on the plywood pieces. The upper and lower chains in frictional contact with the veneer sections are driven, in the direction indicated by the arrow, by any suitable means. The thin veneer sheets 2, 3 and 4 are thus caught between the chains and crowded sidewise into close edge-to-edge contact with one another as they enter the adhesive application section. At this point, the crowding action forces the sections forward in-line and to all intents and purposes as a unitary sheet underneath adhesive applicator supporting means 5.

Numeral 6 designates a hot melt adhesive applicator and reservoir which pumps hot melt adhesive from the tank through conduits 7, 8, 9 and 10 which are attached, rspectively, to adhesive applicator nozzles 11, l2, l3 and 14. The molten adhesive passes from nozzles 11, I2, 13 and 14 and falls by gravity onto the upper surface of each of the random width veneer sections as a plurality of parallel adhesive beads l5, l6, l7 and 18 as shown.

Also mounted on supporting means 5 is a shaft 19 freely rotating in bearings 20 and 21. Spools or rolls of porous paper tape 22, 23, 24 and 25 are detachably mounted on this shaft in such manner that the tapes running therefrom will be caught between the pinch of roll 26 and the surfaces of the moving succession of veneer sections at points directly in contact with the respective adhesive beads.

Roll 26 is a pressure roll which is spring or weight loaded (by means not shown) and may be heated or cooled depending upon the requirements of any specific operation. This roll also functions to distribute the respective beads of adhesive over the under surface of the tapes and also to force the molten adhesive into any irregularities which may exist in the upper surfaces of the wood veneer sections as they pass underneath the roll.

The adhesively joined tape material then passes underneath chopper 28 where it is cut into 8 foot lengths by a shearing knife (not shown). As it emerges from chopper 28, the 8 foot lengths are cut in the center by saw 29 to give 4 X 8 foot sections of finished plywood veneer cores. The sheets of core material are then lifted off the supporting means by conventional vacuum lifters (not shown) and stacked in stacks 30 and 31 for subsequent use in a plywood laminating operation.

Referring to FIGS. 2 and 3 these illustrate typical plywood products which have been fabricated by employment of the improved core material of the invention. In FIG. 2 numeral 32 designates a plywood core produced in accordance with the invention interposed between and glued to plywood sheets or plys 33 and 34. Likewise, in FIG. 3 numerals 32a and 32b designate similar cores glued between

plywood pieces

35, 36 and 37 in a five layer combination. In both of these products, it should be noted that the upper surfaces of the face plys are perfectly free from ridges or other surface irregularities sometimes telegraphed to the surface of such products when the multi-section core veneers are produced by the use of prior art veneer section joining means such as adhesive-impregnated strings and the like.

According to one broader aspect of this invention, there is provided a method of continuously making multi-sectional plywood veneer core sheets having substantially uniform dimensions from substantially rectangular sectional sheets having random dimensions comprising the steps of:

a. continuously passing in a forwardly in-line direction a succession of thin random width substantially rectangular wood veneer sections of substantially the same length measured perpendicularly to the in-line direction, whereby said sections come into in-line, edge-to-edge contact with one another, thereby forming a succession of abutting sections,

b. continuously depositing at spaced intervals a plurality of continuous beads of molten hot melt adhesive on the upper surfaces of each of the succession of abutting sections in lines parallel to the in-line direction,

c. pressing a paper tape into contact with each of the adhesive beads, while still soft, whereby the adhesive is spread across the under surface of each tape and into intimate contact with the adjacent wood surfaces of the abutting sections,

d. solidifying the adhesive to form a strong adhesive bond between the tapes and the abutting sections, whereby the sections are firmly held together inline as a substantially unitary plywood veneer core sheet, and

e. cutting the unitary sheet into a plurality of multisectional plywood veneer core sheets having substantially uniform dimensions.

According to another of the broader aspects of this invention, there is provided a method of continuously making multi-sectional plywood veneer core sheets having substantially uniform dimensions from substantially rectangular sectional sheets having random dimensions comprising the steps of:

a. continuously passing in a forwardly in-line direction a succession of this random width substatially rectangular wood veneer sections of substantially the same length measured perpendicularly to the in-line direction, whereby said sections come into in-line, edge-to-edge contact with one another, thereby forming a succession of abutting sections,

b. continuously feeding a plurality of paper tapes, each of which is coated on one surface with a hot melt adhesive in normally solid form,

c. heating the adhesive on each tape whereby it is softened to form an adhesive surface on each heated tape,

d. continuously depositing at spaced intervals a plurality of heated tapes on the upper surfaces of each of the succession of abutting sections in lines parallel to the in-line direction,

pressing the adhesive surface of each heated tape into intimate contact with the adjacent wood surface of the abutting sections,

f. solidifying the adhesive to form a strong adhesive A multi-section thin wood veneer plywood core is prepared in accordance with that embodiment of the invention which involves first laying down beads of a hot melt adhesive on the upper wood surfaces of a plurality of random width veneer sections in contact inline and edge-to-edge, followed by superimposition of paper tapes on the respective adhesive beads and employing an apparatus and procedure such as that illustrated in FIG. 1 of the drawings, as follows:

A hot melt adhesive blend having a Brookfield viscosity of 2,000 20,000 centipoises at 350F. composed of percent by weight of polyethylene having a molecular weight of 8,000 12,000 and 30 percent by weight of a polyterpene resin is heated to molten condition at a temperature of 350 400F. This blend is applied in l/16 /a inch diameter beads to thin wood veneer plys, which are approximately 8 feet in length but of random widths and crowded together in in-line and edge to-edge contact as they are conveyed in'line onto the horizontal upper surface of an endless belt conveyor driven at a linear speed of 40 feet per minute. As the beads are laid onto the upper veneer surface continuous /2 inch wide porous paper tapes having a tensile strength and tear resistance sufficient to withstand the stresses incident to subsequent handling of the joined material without rupture or tearing are laid down on top of each bead. These tapes are pressed by a weighted roller directly onto the beads of molten adhesive these are laid down. Under the applied pressure the adhesive is forced into and fills the irregularities in the wood surfaces and simultaneously, by filling the pores of the paper tape, effects a strong bond between wood, adhesive and paper. In general, at least four adhesive bead-paper strip combinations are laid onto the veneer sections as shown in FIG. 1. The resulting core material is then cut into 4 X 8 foot integral sections which are capable of being handled with the same facility as full face veneers. These sections are continuously removed from the conveyor and stacked for use in any desired subsequent plywood laminating operation.

EXAMPLE 2 This example illustrates the preparation of a multisection thin wood veneer core in accordance with that embodiment of the invention in which the step of first laying down of adhesive beads on the upper surfaces of the random width veneer sections is omitted and tapes, each of which is precoated with the adhesive, are continuously fed into contact with the upper surfaces of the veneer sedctions and the adhesive reactivated in situ by heat and pressure. Proceeding in accordance with this embodiment, four l-inch wide porous paper tapes coated on one side with a 3 mil layer of hot melt adhesive, of the same composition as that described in Example 1, are passed from supply rolls, detachably mounted on a shaft in the same manner as tape rolls 22, 23, 24 and 25 of FIG. 1 into contact with a pressure roll (similar to roll 26 of FIG. 1) maintained at a temperature of 400F. by any appropriate internal heating means.

The precoated tapes are passed into contact with the heated roll with the uncoated surface of each tape in contact with the roll. When operating-in this manner the shaft carrying the precoated tape supply rolls will be positioned a short distance forward of and above the heated roll to enable each of the tapes to contact the surface of the roll for a sufficient time to permit transmitted heat to melt the adhesive coating on each tape before it passes underneath the roll and into contact with the wood surfaces of the veneer sections. Upon emerging from underneath the pressure roll, the molten adhesive underlying each tape will be solidified by the cooling effect of the surrounding air or by positive cooling means, if desired, In any event, strong bonds are produced between the tapes and the wood surfaces, thus providing what is to all intents and purposes a unitary thin veneer core structure. After cooling the material is passed into a cutter section and cut into 4 X 8 foot pieces in the same manner as described in Example I, removed from the process and stacked for use in any desired plywood laminating operation.

It will be evident from the above description and examples that we have provided a simple, efficient, economical, easily operable and practical method for the manufacture of plywood cores or centers by joining random width sections of thin wood veneers and that this method avoids such disadvantages as have been referred to above, particularly the formation of ridges or other unsightly defects in the final plywood product and the occurrence of areas of incomplete adhesion. The method of the invention is particularly characterized by the fact that it is readily adaptable to plywood core manufacturing operations as presently practiced in the industry core manufacturing operations as presently practiced in the industry and for such adaptation requires a minimum of alteration in existing machinery. Many other advantages will be apparent to those skilled in the art.

Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected without departing from the spirit and scope of the invention as described hereinabove.

We claim:

1. Method of continuously making multi-sectional plywood veneer core sheets having substantially uniform dimensions from substantially rectangular sectional sheets having random dimensions comprising the steps of:

a. continuously passing in a forwardly in-line direction a succession of this random width substantially rectangular wood veneer sections of substantially the same length measured perpendicularly to the in-line direction, whereby said sections come into in-line, edge-to-edge contact with onne another, thereby forming a succession of abutting sections,

2. Method of continuously making multi-sectional plywood veneer core sheets having substantially uniform dimensions from substantially rectagular sectional sheets having random dimensions comprising the steps of:

d. continuously depositing at spaced intervals a plu- I rality of heated tapes on the upper surfaces of each of the succession of abutting sections in lines parallel to the in-line direction,

e. pressing the adhesive surface of each heated tape into intimate contact with the adjacent wood surface of the abutting sections,

. solidifying the adhesive to form a strong adhesive bond between the tapes and the abutting sections. whereby the sections are firmly held together inline as a substantially unitary veneer core sheet, and

g. cutting the unitary sheet into a plurality of multisectional plywood veneer core sheets having substantially uniform dimensions.

3. Method of claim 1 in which the hot melt adhesive is a blend of low molecular weight polymers having a Brookfield viscosity of 2,000 20,000 centiposes at 350F. and composed of percent by weight of polyethylene having a molecular weight of 8,000 12,000 and 30 percent by weight of a polyterpene resin.

4. Method of claim 3 in which the hot melt adhesive is applied to the succession of abutting veneer sections at a melt temperature of 300 450F.

5. Method of claim 2 in which the hot melt adhesive coating on the paper tapes is a blend of low molecular weight polymers having a Brookfield viscosity of 2,000 20,000 centipoises at 350F and composed of 70 percent by weight of polyethylene having a molecular weight of 8,000 12,000 and 30 percent by weight of a polyterpene resin.

Claims

1. METHOD OF CONTINUOUSLY MAKING MULTI-SECTIONAL PLYWOOD VENEER CORE SHEETS HAVING SUBSTANTIALLY UNIFORM DIMENSIONS FROM SUBSTANTIALLY RECTANGULAR SECTIONAL SHEETS HAVING RANDOM DIMENSIONS COMPRISING THE STEPS OF: A. CONTINUOUSLY PASSING IN A FORWARDLY IN-LINE DIRECTION A SUCCESSION OF THIS RANDOM WIDTH SUBSTANTIALLY RECTANGULAR WOOD VENEER SECTIONS OF SUBSTANTIALLY THE SAME LENGTH MEASURED PERPENDICULARLY TO THE IN-LINE DIRECTION, WHEREBY SAID SECTIONS COME INTO IN-LINE, EDGE-TO-EDGE CONTACT WITH ONE ANOTHER, THEREBY FORMING A SUCCESSION OF ABUTTING SECTIONS, B. CONTINUOUSLY DEPOSITING AT SPACED INTERVALS A PLURALITY OF CONTINUOUS BEADS OF MOLTEN HOT MELT ADHESIVE ON THE UPPER SURFACES OF EACH OF THE SUCCESSION OF ABUTTING SECTIONS IN LINES PARALLEL TO THE IN-LINE DIRECTION, C. PRESSING A PAPER TAPE INTO CONTACT WITH EACH OF THE ADHESIVE BEADS, WHILE STILL SOFT, WHEREBY THE ADHESIVE IS SPREAD ACROSS THE UNDER SURFACE OF EACH TAPE AND INTO INTIMATE CONTACT WITH THE ADJACENT WOOD SURFACES OF THE ABUTTING SECTIONS,

2. Method of continuously making multi-sectional plywood veneer core sheets having substantially uniform dimensions from substantially rectagular sectional sheets having random dimensions comprising the steps of: a. continuously passing in a forwardly in-line direction a succession of thin random width substantially rectangular wood veneer sections of substantially the same length measured perpendicularly to the in-line direction, whereby said sections come into in-line, edge-to-edge contact with one another, thereby forming a succession of abutting sections, b. continuously feeding a pluRality of paper tapes, each of which is coated on one surface with a hot melt adhesive in normally solid form, c. heating the adhesive on each tape whereby it is softened to form an adhesive surface on each heated tape, d. continuously depositing at spaced intervals a plurality of heated tapes on the upper surfaces of each of the succession of abutting sections in lines parallel to the in-line direction, e. pressing the adhesive surface of each heated tape into intimate contact with the adjacent wood surface of the abutting sections, f. solidifying the adhesive to form a strong adhesive bond between the tapes and the abutting sections, whereby the sections are firmly held together in-line as a substantially unitary veneer core sheet, and g. cutting the unitary sheet into a plurality of multi-sectional plywood veneer core sheets having substantially uniform dimensions.

3. Method of claim 1 in which the hot melt adhesive is a blend of low molecular weight polymers having a Brookfield viscosity of 2,000 - 20,000 centiposes at 350*F. and composed of 70 percent by weight of polyethylene having a molecular weight of 8,000 - 12, 000 and 30 percent by weight of a polyterpene resin.

4. Method of claim 3 in which the hot melt adhesive is applied to the succession of abutting veneer sections at a melt temperature of 300* - 450*F.

5. Method of claim 2 in which the hot melt adhesive coating on the paper tapes is a blend of low molecular weight polymers having a Brookfield viscosity of 2,000 - 20,000 centipoises at 350*F and composed of 70 percent by weight of polyethylene having a molecular weight of 8,000 - 12,000 and 30 percent by weight of a polyterpene resin.