US2545603A - Paper-covered wood product and method of making same - Google Patents

Description

March 20, 1951 R. J. BYERS ET AL PAPER-COVERED WOOD PRGDUCT AND METHOD OF MAKING SAME Filed Dec. 22, 1947 EVENT [7P5 leap/v 1/ flaws Moss 5. (km/12m Patented Mar. 20, 1951 PAPER-COVERED WOOD PRODUCT AND' METHOD OF MAKING SAME Ralph J. Byers, Chicago, Ill., and Moss. B. Christian, Tallulah, La., assignors to Chicago Mill and Lumber Company, Chicago, Ill., a. corporation of Delaware Application December 22, 1947, Serial No. 793,232.

Claims.

This. invention relates to the production of a dry, laminated paper and expanded Wood veneer product formed from bonded-together wet,

swollen wood veneer and wet, expanded paper.

Specifically, the invention includes a papercovered expanded wood veneer product and a method of making the product from wet wood, wet paper, and wet glue, wherein the laminated assembly is dried only after the glue. bond is sufiiciently strong to prevent slippage between the paper and wood so that the paper will hold the wood in the expanded condition of its wet state.

This application is a continuation in part of. our copending application entitled: Veneer and Method of Making Same, Serial No. 561,628, filed November 2, 1944, now Patent No. 2,442,115, granted May 25, 1948.

According to this invention, any species of wood, including woods that were heretofore unfit for use except as ,fuel, in its green, undried, and swollen state, is lathe-cut or peeled into a thin veneer sheet and is covered on both sides with sheets ofwet, expanded paper that have been coated with an alkalinized cold-setting, water-resistant protein-type glue such as a sore bean glue or a locust bean glue. The glue has a relatively high pH value (above '7) which reduces the surface tension of the glue coating on the paper permitting water in the glue to be rapidly absorbed into the paper. The water in the glue causes the paper to expand and stretch and, in order to balance the expansion of both faces of the paper, the unglued face of the paper is moistened, preferably with a wax emulsion, although water alone can be used. The glue-coated faces of the paper sheets are pressed against the veneer faces under suflicient pressures to firmly contact the paper with the wood. The glue then sets rather rapidly because of absorption of some of its water content by the paper, but the wood is not dewatered below 30% moisture content. A strong bond is formed so that slippage between the paper and wood cannot occur. The assembly isthen subjected to an increased pressure which will squeeze water out of the wood into the paper to equalize or balance the moisture content of the wood and paper. This heavy pressure treatment will not affect the glue bond. After the heavy pressure treatment, the assembly is passed through a drying kiln where it is dried to a moisture content between 6 to 12 The term moisture content as used herein and in the claims is based upon the oven dry weight of the wood and, when expressed in-terms 01' percentage, means the weight of the water present in the material divided by the oven dry weight (bone dry Weight) of the material multiplied by 100. Thus, it the moisture-laden wood sample weighed 10 lbs., and, when oven dried to a bone dry basis, it weighed 5 lbs., its moisture content, would be determined as follows:

Normally, wood beginsto shrink as its moisture content is reduced below 30% and the shrinkage of wood from a green, wet state to a dry state averages about 10%. Further, normal shrinkage of wood brings about the formation of cracks and splits because the stronger bundled fiber portions will pull away from the weaker bundled portions as shrinking progresses. The present invention minimizes this shrinkage and this cracking and splitting of wood, because the paper, which is bonded to the Wood While it is Still in its wet, swollen condition, will hold the Wood in it panded condition even after the moisture is driven therefrom. The product of the invention therefore includes a wood veneer core with t e Wood in an open mesh expanded condition free from splits or cracks.

It is, accordingly, an object of this invention to provide a laminated paper and wood product wherein the wood is substantially dry but held in an unshrunk condition by the paper and the non-slipping bond between the paper and the wood.

Another obj ct of the invent on is t provide a paper-covered wood veneer product from green, undried wood, wet, expanded paper, and wet glue without permitting the wood to shrink substantially as the product is dried to a moisture content between 6 to 12%.

Another object of the invention is to provide a method of making paper-covered wood veneer from any species of green or wet wood including heretofore unusable woods, and paper which holds the wood in its expanded green state form even after the assembly is dried.

A specific object of the invention is to provide paper-covered wood veneer composed of tough kraft paper, wood veneer, and a water-resistant glue bond coacting with the paper to hold the wood in an expanded condition.

A further object of the invention is to produce a paper-covered wood veneer product free from splits, cracks, loose knots, and other defects normally present in dry wood veneer.

Other and iilrther objects of the invention will become apparent to those skilled in the art from the following description and from the annexed 3 sheet of drawings forming a part of this specification.

On the drawings:

Figure l is a somewhat diagrammatic side elevational view illustrating the method of this invention for making the paper-covered wood product of this invention.

Figure 2 is a plan view of the product of this invention with successive layers partially removed to show underlying layers.

Figure 3 is a cross-sectional view of the product taken along the line III-III of Figure 2.

Figure 4-. is a plan view of a veneer sheet, onehalf of which is covered with paper in accordance with this invention, and illustrating the manner in which the paper holds the wood veneer against shrinkage.

As shown on the drawings:

As illustrated in Figure l, a green wood log I is revolved against a suitable broad knife blade cutter i I of a veneer cutting lathe to form a thin green wood veneer sheet or ribbon H. The log [0 is in its green, undried condition and may even have live sap flowing therein. The log has a moisture content above 30%, because most Woods begin to shrink a their moisture content drops below 30 Usually the moisture content of the log will average about 130%. Woods such as gum, oak, cottonwood, sycamore, pine, and fir are examples of satisfactory species of wood to form the product of this invention. Woods that otherwise were unusable except for fueLzsuch as overcup white oak, are now rendered useful in veneer making. Heretofore such white oak woods checked and split to such an extent when being dried that they were totally unfit for veneers and plywood panels.

The veneer sheet or ribbon I2 is quite thin and may have a thickness varying from .01 to 1% inch, with the thinner sheets in this range being the most economical. The veneer l2 has the grain running crosswise or transversely of the sheet or ribbon. If necessary, pieces of veneer are stitched or stapled together to form a continuous sheet or ribbon i2.

Continuous sheets l3, (3 of unsized dry finish Fourdrinier kraft paper are unwound from rolls M and [5 respectively positioned above and below the veneer sheet E2. The sheet l3 from the roll l4 passes over a coating roller I'G of a coating machine ll which applies an aqueous paraffin wax emulsion to the underface of the sheet. The sheet then travels under a coating roll l8 of a second coating machine [9 to receive, on its top face, a water solution of a soya bean glue. The sheet then passes around a turning roll 2!] and has the adhesived face thereof deposited on top of the veneer [2 as the sheet passes under a roll 2|.

The sheet l3 from the roll [5 passes around a turning roll 22 and thence over a coating roll 23 of a coating machine 24 which deposits an aqueous wax emulsion on one face of the sheet. The sheet then travels around guide rolls 25 to the, coating roll 26 of a second coating machine 21 which adhesive-coats the opposite face of the sheet with the soya bean glue. The adhesived sheet then passes around a turning roll 28 and is pressed against the underface of the veneer ribbon [2 by means of a roll 29.

The Fourdrinier kraft paper is tough, waterabsorptive, and of a type commonly used for liner board. The fibers of the paper run lengthwise of the sheet and thus the fibers of the wood and paper are at substantially right angles to each 4 other. The kraft paper weighs from 26 to lbs. per thousand square feet, and a 42-lb. paper is a preferred average.

The wax emulsion deposited on the sheet by the coating machines I1 and 24 is composed of paraffin wax and water in suitable emulified condition. The wax is used to impart a smooth finish to the outer face of the paper but it is not essential to this invention. The water of the emulsion moistens the outer faces of the sheet l3 so that the Water from the glue, which is applied to the inner faces of the sheets, will not unevenly expand the paper causing it to curl and buckle. From 2 to 10% of water, based on the Weight of the paper, is added to the outer faces of the sheets by the coating machines I! and 24 with 5% forming a preferred average.

The soya bean glue applied to the inner faces of the sheets by the coating machines I9 and 21 is composed of soya bean flour of a relatively fine mesh, water, and caustic soda in sufficient amounts to form a soya bean glue. From 30 to of water, based on the weight of the paper, is added by the glue to the inner faces of the paper sheet, with about 80% forming a desired average. The caustic soda gives the glue a high pH value, reducing its surface tension and speeding up absorption of water from the glue film into the paper. This water absorption, in turn, speeds up setting of the glue.

The paper sheets I3, wet on both faces by water in the wax emulsion and water in the glue, will expand and stretch, and a sufficient amount of time elapse from the water application to the point of deposition of the adhesive-coated faces of the paper on the veneer ribbon l2 so that the paper can expand.

The total moisture content in the paper preferably balances the total moisture content of the wood and the glue preferably applies more moisture to the inner face of the paper than the wax emulsion applies to the outer face of the paper.

The paper covered veneer ribbon passes from the first pair of squeeze rolls, composed of rolls 2| and 29, between a series of small diameter press rolls 30. These press rolls are not driven. From the small diameter rolls 30, the assembly passes between larger diameter driven press rolls 3!. The press rolls 3liapply a pressure of about 7 lbs.

per square inch on the assembly while the larger diameter driven press rolls 3! apply. pressures within the range of '75 to lbs. per square inch on the assembly. These press rolls 3!] and 31 firmly press the paper against the Wood and insure good bonding contact between the paper and wood. The rolls 3!! and 3| are unheated and suf-. ficient time elapses during the passage of the assembly through these rolls so that the soya bean glue can cold set to a point where a bond is formed that will prevent relative slippage between the paper and wood. The cold bond is actually stronger than the paper itself, so that slippage, cannot possibly occur. 7

The heavy pressure rolls 3! are effective tosqueeze water out of the wood and equalize the- Water contents of the wood and paper. For example, the paper may lose moisture by evapora-- tion as it passes from the coating machine through the pressure rolls 30, and the high pres-" sure rolls 3| will drive moisture out of the wood into the paper to compensate for this loss of. moisture by evaporation.

bon is cut by a cutter 32 into panels 33 of the desired length; These panels are fed by a conveyor '34 to a drying kiln '35 where they pass between pressing rolls 36 so that the laminated assembly is hot pressed after the cold pressing operation. The drying kiln has an inlet temperature of about 250 F. and an outlet tem-. perature of about 375 F. .The panels 33 are dried to a moisture content between 6 to 12%, and preferably to a moisture content of 8%. The finished product 31 issuing from the drying kiln '35 has substantially the same dimensions as the original wet material from which it was formed. Shrinkages averaging 1.5% or less are encountered, and these shrinkages are represented by uniform shrinking of the expanded wood and expanded paper so that puckering and wrinkling of the paper does not occur. This shrinkage is less than of the normal shrinkage of wood from its green, wet stage to its dry state.

' As shown in Figures 2 and 3, the product 3'! is composed of an intermediate sheet or .core 38 of wood veneer which is dry, but still in the expanded swollen condition of its green state. Thus the veneer is full of pores 38a that were formerly filled with water, but is free from cracks, splits, or checks normally present in dried wood. Any knots, such as 38b, are tight in the body of the wood, because the wood has not shrunk away from the knots. Both faces of the wood core 38 are covered with paper sheets 39. These paper sheets 39 have smooth, glazed outer faces 390. containing wax from the emulsion. Glue bonds 4B firmly unite the inner faces of the sheets 38 to the wood core. Some of the glue penetrates into the core and paper, but does not bleed completely through the paper.

As illustrated in Figure 4, the paper faces 39 hold the wood core against shrinkage. Thus the half portion of the core which is uncovered by the paper is in a shrunken, dried condition, full of cracks and splits 380, while the papercovered portion of the veneer is uniformly porous. The grain of the paper extends along the length of the ribbon and is at right angles to the grain of the wood core so that the cross-banding effect of plywood is obtained.

The paper-covered wood veneer of this invention has a tensile strength of almost three times the tensile strength of the veneer wood from which it is formed. It has a puncture resistance of almost four times the resistance of the uncovered veneer wood. The product is nailable and sawable in the same manner as plywood or lumber, and is especially useful in the production of boxes and crates. The soya bean glue when dried forms a bond which is water resistant and the product will effectively resist weather conditions. The uniform moisture content of 6 to 12% in the finished product prevents buckling and warping irrespective of atmospheric humidity changes.

From the above descriptions it should be understood that this invention provides a papercovered wood veneer according to a continuous method from wet green wood, wet glue, and wet paper, which prevents shrinkage of the wood so that the finished dry product maintains substantially the same dimensions as the green wood from which it is formed.

It will, of course, be understood-that various details of the product and method may be varied through a wide range without departing from the principles of this invention and it is, therefore, not the purpose to limit the patent granted hereonothe'rwise than necessitated by the scope of the appended claims.

- We claim as our invention:

l. A composite board formed from green woo having a moisture content above 30%, flexible absorbent paper, and a water-resistant glue, which comprises a dry wood veneer sheet containing from 6 to 12% moisture but remaining in the swollen green wood expanded condition, a sheet of absorbent paper united to said veneer sheet and containing moisture absorbed from the wood, said paper having a moisture content of about 6 to 12%, and an alkalinized cold set waterresistant protein glue bond fixedly uniting the paper and wood in non-slipping relation and causing the paper to hold the wood in the expanded form.

2. A pliable veneer panel which comprises a sheet of wood veneer containing from 6 to 12% moisture but having the cells thereof in the swollen expanded form of green wood, a sheet of unsized tough kraft paper covering each face of the veneer, an alkalinized soya bean glue fixedly uniting the paper sheets with the veneer in non-slipping relation and causing the paper to hold the wood in the expanded condition, said soya bean glue having a pH value above 7 and effective to reduce the surface tension of the glue coating on the paper to facilitate absorption of the glue into the paper, and a wax surface on theouter faces of the paper sheets providing a smooth finish to the surfaces of the panel.

3. The method of making a laminated board which comprises providing a sheet of Wet wood veneer containing more than 30% moisture, applying moisture to one face of each of two sheets of paper, applying to the opposite face of each of said sheets of paper an aqueous alkaline glue solution capable of forming a non-slipping bond between the paper and wood prior to removal of the moisture from the wood, allowing the paper to expand, pressing the glued face of one sheet of the expanded paper against one face of the wood veneer, pressing the glued face of the other sheet of the expanded paper against the opposite face of the wood veneer and thereby firmly contacting the glue with both faces of the wood, setting the glue before the wood begins to shrink to form a non-slipping bond between the paper and the unshrunk wood, subjecting the assembly to increased pressure to squeeze water from the wood into the paper for balancing the moisture conditions of the wood and the paper, and drying the laminated assembly to a moisttu e content between 6 to 12% whereby the non-slipping bond between the paper and wood will cause the paper to hold the wood in its open mesh expanded swollen condition even after the moisture content of the wood is reduced below the point where the wood normally begins to shrink.

4. The method of making paper-covered wood veneer from green wood veneer containing more than 30% moisture which comprises moistening one face of each of two sheets of tough paper with water, applying to the other face of each of said two sheets of paper a water solution of a soya bean glue capable of forming a non-slipping bond between the paper and green wood prior to removal of the moisture from the green wood, allowing the moistened sheets to expand, depositing the glued face of one expanded sheet on one face of the green wood veneer, depositing the glued face of the other expanded sheet'on the opposite face of said green wood veneer, pressing 76 both sheets of the paper against the green WOOd veneer to firmly contact the glue with both the paper and the wood, setting the glue before the moisture content of the wood is reduced below 30% and thereby uniting the wood and paper in non-slipping relation, further pressing the assembly to squeeze water from the wood into the paper for balancing the moisture conditions of the wood and paper, and drying the assembly to a moisture content between 6 to 12% and thereby further setting the glue, whereby the paper will hold the wood in its expanded swollen green wood form.

5. The method of making paper-coveredwood veneer from a ribbon of green wood veneer containing more than 30% moisture which comprises coating one face of each of two sheets of tough kraft paper with an aqueous wax emulsion, coating the opposite face of each of said two sheets of paper with an aqueous soya bean glue capable of forming a non-slipping bond between the paper and the ribbon of green wood prior to removal of the moisture from the wood, allowing the sheets of paper to expand due to the increased moisture content added thereto by the Wax emulsion and the glue, depositing the glue-coated face of one of said expanded paper sheets on a face of the green Wood veneer, depositing the gluecoated face of the other of said expanded sheets of paper on the opposite face of said green wood veneer, pressing the assembly together to firmly unite the paper and wood before the wood begins to shrink, setting the glue to form a non-slipping bond between the paper and the wood while the woodstill has a moisture content over 30%, subjecting the assembly to increased pressures for squeezing moisture from the wood into the paper, and thereafter drying the assembly to a moisture content between 6 to 12% while said paper holds the wood in its expanded green wood condition.

RALPH J. BYERS. MOSS B. CHRISTIAN.

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

UNITED STATES PATENTS Number Name Date 1,125,973 Davidson Jan. 26, 1915 1,369,743 Hood et a1. Feb. 22, 1921 1,714,858 Elmendorf May 28, 1929 1,714,859 Elmendorf May 28, 1929 1,997,344 Randall et al. Apr. 9, 1935 1,999,253 Norris Apr. 30, 1935 2,095,389 Kondolf Oct. 12, 1937 2,271,620 Brier et al Feb. 3,1942 2,325,584 Barnhart Aug. 3, 1943 2,372,617 Trew L Mar. 27, 1945 2,425,660 Ware et al. Aug. 12, 1947 2,442,115 Byers et al May 25, 1948

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